Premium SKU (#30396)

* Added premium SKU

* removed duplicate enterprise license check functions

* Added license check on API layer

* lint fix

* lint fix

* refactured signature:

* test: Add comprehensive tests for license tier check functions

* fixed test

* text update

* optimised license checks

* fixedf test

* Updated license valid function

* webapp license checks

* handling prekium SKU in webappp:

* added plugin api method and general refactoring

* Updated tests

---------

Co-authored-by: Mattermost Build <build@mattermost.com>

server/channels/api4/channel.go

@@ -2453,7 +2453,7 @@ func convertGroupMessageToChannel(c *Context, w http.ResponseWriter, r *http.Req
 }
 
 func canEditChannelBanner(license *model.License, originalChannel *model.Channel) *model.AppError {
-	if license == nil || !license.IsE20OrEnterprise() {
+	if !model.MinimumPremiumLicense(license) {
 		return model.NewAppError("", "license_error.feature_unavailable", nil, "feature is not available for the current license", http.StatusForbidden)
 	}