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.

internal/feature/feature.go

@@ -8,6 +8,7 @@ const (
 	KeyLoginDefaultOrg
 	KeyTriggerIntrospectionProjections
 	KeyLegacyIntrospection
+	KeyUserSchema
 )
 
 //go:generate enumer -type Level -transform snake -trimprefix Level
@@ -27,4 +28,5 @@ type Features struct {
 	LoginDefaultOrg                 bool `json:"login_default_org,omitempty"`
 	TriggerIntrospectionProjections bool `json:"trigger_introspection_projections,omitempty"`
 	LegacyIntrospection             bool `json:"legacy_introspection,omitempty"`
+	UserSchema                      bool `json:"user_schema,omitempty"`
 }