XYZ-37: Advanced Permissions Phase 1 Backend. (#8159)

* XYZ-13: Update Permission and Role structs to new design.

* XYZ-10: Role store.

* XYZ-9/XYZ-44: Roles API endpoints and WebSocket message.

* XYZ-8: Switch server permissions checks to store backed roles.

* XYZ-58: Proper validation of roles where required.

* XYZ-11/XYZ-55: Migration to store backed roles from policy config.

* XYZ-37: Update unit tests to work with database roles.

* XYZ-56: Remove the "guest" role.

* Changes to SetDefaultRolesFromConfig.

* Short-circuit the store if nothing has changed.

* Address first round of review comments.

* Address second round of review comments.

model/cluster_message.go

@@ -21,6 +21,7 @@ const (
 	CLUSTER_EVENT_INVALIDATE_CACHE_FOR_CHANNEL                      = "inv_channel"
 	CLUSTER_EVENT_INVALIDATE_CACHE_FOR_USER                         = "inv_user"
 	CLUSTER_EVENT_CLEAR_SESSION_CACHE_FOR_USER                      = "clear_session_user"
+	CLUSTER_EVENT_INVALIDATE_CACHE_FOR_ROLES                        = "inv_roles"
 
 	CLUSTER_SEND_BEST_EFFORT = "best_effort"
 	CLUSTER_SEND_RELIABLE    = "reliable"