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.

api4/api.go

@@ -96,6 +96,8 @@ type Routes struct {
 
 	Reactions *mux.Router // 'api/v4/reactions'
 
+	Roles *mux.Router // 'api/v4/roles'
+
 	Emojis      *mux.Router // 'api/v4/emoji'
 	Emoji       *mux.Router // 'api/v4/emoji/{emoji_id:[A-Za-z0-9]+}'
 	EmojiByName *mux.Router // 'api/v4/emoji/name/{emoji_name:[A-Za-z0-9_-\.]+}'
@@ -194,6 +196,8 @@ func Init(a *app.App, root *mux.Router, full bool) *API {
 
 	api.BaseRoutes.OpenGraph = api.BaseRoutes.ApiRoot.PathPrefix("/opengraph").Subrouter()
 
+	api.BaseRoutes.Roles = api.BaseRoutes.ApiRoot.PathPrefix("/roles").Subrouter()
+
 	api.InitUser()
 	api.InitTeam()
 	api.InitChannel()
@@ -219,6 +223,7 @@ func Init(a *app.App, root *mux.Router, full bool) *API {
 	api.InitWebrtc()
 	api.InitOpenGraph()
 	api.InitPlugin()
+	api.InitRole()
 
 	root.Handle("/api/v4/{anything:.*}", http.HandlerFunc(Handle404))