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/command/instance_features.go

@@ -15,12 +15,14 @@ type InstanceFeatures struct {
 	LoginDefaultOrg                 *bool
 	TriggerIntrospectionProjections *bool
 	LegacyIntrospection             *bool
+	UserSchema                      *bool
 }
 
 func (m *InstanceFeatures) isEmpty() bool {
 	return m.LoginDefaultOrg == nil &&
 		m.TriggerIntrospectionProjections == nil &&
-		m.LegacyIntrospection == nil
+		m.LegacyIntrospection == nil &&
+		m.UserSchema == nil
 }
 
 func (c *Commands) SetInstanceFeatures(ctx context.Context, f *InstanceFeatures) (*domain.ObjectDetails, error) {