Add User Info to created tasks (#303)

This PR makes user information from JWT tokens available as part of a Task.

Included changes:
* Renamed `verify_token` to `call_if_agent`, since this function is specific to agent token verification
* Renames `is_authorized` to `is_agent`, since this function checks if the token is an agent
* Adds support for unmanaged nodes in `is_agent` (see #133 for information) 
* Saves the user information from the JWT token on task create as part of `TaskConfig`

Note, `TaskConfig` is what is provided to notification templates.  This enables Github issues and ADO work items to tie back to the user that created the task.

Note, while `upn` _usually_ means email for AAD user tokens.  If we were going to make use of the email address, we should perform a graph lookup based on the `oid`, but we're not.

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

@@ -231,7 +231,7 @@ def build_message(
         WebhookMessage(
             webhook_id=webhook_id, event_id=event_id, event_type=event_type, event=event
         )
-        .json(sort_keys=True)
+        .json(sort_keys=True, exclude_none=True)
         .encode()
     )
     digest = None