feat: implement user schema management (#7416)

This PR adds the functionality to manage user schemas through the new user schema service.
It includes the possibility to create a basic JSON schema and also provides a way on defining permissions (read, write) for owner and self context with an annotation.

Further annotations for OIDC claims and SAML attribute mappings will follow.

A guide on how to create a schema and assign permissions has been started. It will be extended though out the process of implementing the schema and users based on those.

Note:
This feature is in an early stage and therefore not enabled by default. To test it out, please enable the UserSchema feature flag on your instance / system though the feature service.

cmd/defaults.yaml

@@ -832,7 +832,7 @@ DefaultInstance:
       Greeting: Hello {{.DisplayName}},
       Text: The password of your user has changed. If this change was not done by you, please be advised to immediately reset your password.
       ButtonText: Login
-  
+
   # Once a feature is set on the instance (true or false), system level feature settings
   # will be ignored until instance level features are reset.
   Features:
@@ -1016,6 +1016,8 @@ InternalAuthZ:
         - "execution.read"
         - "execution.write"
         - "execution.delete"
+        - "userschema.write"
+        - "userschema.delete"
     - Role: "IAM_OWNER_VIEWER"
       Permissions:
         - "iam.read"