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/websocket_message.go

@@ -42,6 +42,7 @@ const (
 	WEBSOCKET_EVENT_CHANNEL_VIEWED      = "channel_viewed"
 	WEBSOCKET_EVENT_PLUGIN_ACTIVATED    = "plugin_activated"   // EXPERIMENTAL - SUBJECT TO CHANGE
 	WEBSOCKET_EVENT_PLUGIN_DEACTIVATED  = "plugin_deactivated" // EXPERIMENTAL - SUBJECT TO CHANGE
+	WEBSOCKET_EVENT_ROLE_UPDATED        = "role_updated"
 )
 
 type WebSocketMessage interface {