instance wide configuration (#1010)

TODO:
* [x] add setting initial set of admins during deployment

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

@@ -0,0 +1,34 @@
+#!/usr/bin/env python
+#
+# Copyright (c) Microsoft Corporation.
+# Licensed under the MIT License.
+
+from typing import Optional, Tuple
+
+from onefuzztypes.events import EventInstanceConfigUpdated
+from onefuzztypes.models import InstanceConfig as BASE_CONFIG
+from pydantic import Field
+
+from .azure.creds import get_instance_name
+from .events import send_event
+from .orm import ORMMixin
+
+
+class InstanceConfig(BASE_CONFIG, ORMMixin):
+    instance_name: str = Field(default_factory=get_instance_name)
+
+    @classmethod
+    def key_fields(cls) -> Tuple[str, Optional[str]]:
+        return ("instance_name", None)
+
+    @classmethod
+    def fetch(cls) -> "InstanceConfig":
+        entry = cls.get(get_instance_name())
+        if entry is None:
+            entry = cls()
+            entry.save()
+        return entry
+
+    def save(self, new: bool = False, require_etag: bool = False) -> None:
+        super().save(new=new, require_etag=require_etag)
+        send_event(EventInstanceConfigUpdated(config=self))