Use request.CTX instead of *request.Context (#24877)

* Use request.CTX instead of *request.Context

* Fix tests

server/channels/app/slashcommands/command_join.go

@@ -37,7 +37,7 @@ func (*JoinProvider) GetCommand(a *app.App, T i18n.TranslateFunc) *model.Command
 	}
 }
 
-func (*JoinProvider) DoCommand(a *app.App, c *request.Context, args *model.CommandArgs, message string) *model.CommandResponse {
+func (*JoinProvider) DoCommand(a *app.App, c request.CTX, args *model.CommandArgs, message string) *model.CommandResponse {
 	channelName := strings.ToLower(message)
 
 	if strings.HasPrefix(message, "~") {