support multiple corpus accounts (#334)

Add support for sharding across multiple storage accounts for blob containers used for corpus management.

Things to note:

1. Additional storage accounts must be in the same resource group, support the "blob" endpoint, and have the tag `storage_type` with the value `corpus`.  A utility is provided (`src/utils/add-corpus-storage-accounts`), which adds storage accounts. 
2. If any secondary storage accounts exist, they are used by default for containers.
3. Storage account names are cached in memory the Azure Function instance forever.   Upon adding new storage accounts, the app needs to be restarted to pick up the new accounts.

src/api-service/__app__/onefuzzlib/extension.py

@@ -9,17 +9,13 @@ from uuid import UUID
 
 from onefuzztypes.enums import OS, AgentMode
 from onefuzztypes.models import AgentConfig, Pool, ReproConfig, Scaleset
-from onefuzztypes.primitives import Extension, Region
+from onefuzztypes.primitives import Container, Extension, Region
 
-from .azure.containers import (
-    StorageType,
-    get_container_sas_url,
-    get_file_sas_url,
-    save_blob,
-)
+from .azure.containers import get_container_sas_url, get_file_sas_url, save_blob
 from .azure.creds import get_instance_id, get_instance_url
 from .azure.monitor import get_monitor_settings
 from .azure.queue import get_queue_sas
+from .azure.storage import StorageType
 from .reports import get_report
 
 
@@ -95,8 +91,12 @@ def build_scaleset_script(pool: Pool, scaleset: Scaleset) -> str:
         ssh_path = "$env:ProgramData/ssh/administrators_authorized_keys"
         commands += [f'Set-Content -Path {ssh_path} -Value "{ssh_key}"']
 
-    save_blob("vm-scripts", filename, sep.join(commands) + sep, StorageType.config)
-    return get_file_sas_url("vm-scripts", filename, StorageType.config, read=True)
+    save_blob(
+        Container("vm-scripts"), filename, sep.join(commands) + sep, StorageType.config
+    )
+    return get_file_sas_url(
+        Container("vm-scripts"), filename, StorageType.config, read=True
+    )
 
 
 def build_pool_config(pool: Pool) -> str:
@@ -116,14 +116,14 @@ def build_pool_config(pool: Pool) -> str:
     filename = f"{pool.name}/config.json"
 
     save_blob(
-        "vm-scripts",
+        Container("vm-scripts"),
         filename,
         config.json(),
         StorageType.config,
     )
 
     return get_file_sas_url(
-        "vm-scripts",
+        Container("vm-scripts"),
         filename,
         StorageType.config,
         read=True,
@@ -135,24 +135,28 @@ def update_managed_scripts() -> None:
         "azcopy sync '%s' instance-specific-setup"
         % (
             get_container_sas_url(
-                "instance-specific-setup",
+                Container("instance-specific-setup"),
                 StorageType.config,
                 read=True,
                 list=True,
             )
         ),
         "azcopy sync '%s' tools"
-        % (get_container_sas_url("tools", StorageType.config, read=True, list=True)),
+        % (
+            get_container_sas_url(
+                Container("tools"), StorageType.config, read=True, list=True
+            )
+        ),
     ]
 
     save_blob(
-        "vm-scripts",
+        Container("vm-scripts"),
         "managed.ps1",
         "\r\n".join(commands) + "\r\n",
         StorageType.config,
     )
     save_blob(
-        "vm-scripts",
+        Container("vm-scripts"),
         "managed.sh",
         "\n".join(commands) + "\n",
         StorageType.config,
@@ -170,25 +174,25 @@ def agent_config(
     if vm_os == OS.windows:
         urls += [
             get_file_sas_url(
-                "vm-scripts",
+                Container("vm-scripts"),
                 "managed.ps1",
                 StorageType.config,
                 read=True,
             ),
             get_file_sas_url(
-                "tools",
+                Container("tools"),
                 "win64/azcopy.exe",
                 StorageType.config,
                 read=True,
             ),
             get_file_sas_url(
-                "tools",
+                Container("tools"),
                 "win64/setup.ps1",
                 StorageType.config,
                 read=True,
             ),
             get_file_sas_url(
-                "tools",
+                Container("tools"),
                 "win64/onefuzz.ps1",
                 StorageType.config,
                 read=True,
@@ -212,19 +216,19 @@ def agent_config(
     elif vm_os == OS.linux:
         urls += [
             get_file_sas_url(
-                "vm-scripts",
+                Container("vm-scripts"),
                 "managed.sh",
                 StorageType.config,
                 read=True,
             ),
             get_file_sas_url(
-                "tools",
+                Container("tools"),
                 "linux/azcopy",
                 StorageType.config,
                 read=True,
             ),
             get_file_sas_url(
-                "tools",
+                Container("tools"),
                 "linux/setup.sh",
                 StorageType.config,
                 read=True,
@@ -260,7 +264,7 @@ def repro_extensions(
     repro_os: OS,
     repro_id: UUID,
     repro_config: ReproConfig,
-    setup_container: Optional[str],
+    setup_container: Optional[Container],
 ) -> List[Extension]:
     # TODO - what about contents of repro.ps1 / repro.sh?
     report = get_report(repro_config.container, repro_config.path)
@@ -302,7 +306,7 @@ def repro_extensions(
         script_name = "task-setup.sh"
 
     save_blob(
-        "task-configs",
+        Container("task-configs"),
         "%s/%s" % (repro_id, script_name),
         task_script,
         StorageType.config,
@@ -311,13 +315,13 @@ def repro_extensions(
     for repro_file in repro_files:
         urls += [
             get_file_sas_url(
-                "repro-scripts",
+                Container("repro-scripts"),
                 repro_file,
                 StorageType.config,
                 read=True,
             ),
             get_file_sas_url(
-                "task-configs",
+                Container("task-configs"),
                 "%s/%s" % (repro_id, script_name),
                 StorageType.config,
                 read=True,
@@ -333,13 +337,13 @@ def repro_extensions(
 def proxy_manager_extensions(region: Region) -> List[Extension]:
     urls = [
         get_file_sas_url(
-            "proxy-configs",
+            Container("proxy-configs"),
             "%s/config.json" % region,
             StorageType.config,
             read=True,
         ),
         get_file_sas_url(
-            "tools",
+            Container("tools"),
             "linux/onefuzz-proxy-manager",
             StorageType.config,
             read=True,