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/app/post_permission_utils.go

@@ -55,16 +55,14 @@ func postPriorityCheck(
 	}
 
 	if ack := priority.RequestedAck; ack != nil && *ack {
-		licenseErr := model.MinimumProfessionalProvidedLicense(license)
-		if licenseErr != nil {
-			return licenseErr
+		if !model.MinimumProfessionalLicense(license) {
+			return model.NewAppError("", "license_error.feature_unavailable", nil, "feature is not available for the current license", http.StatusNotImplemented)
 		}
 	}
 
 	if notification := priority.PersistentNotifications; notification != nil && *notification {
-		licenseErr := model.MinimumProfessionalProvidedLicense(license)
-		if licenseErr != nil {
-			return licenseErr
+		if !model.MinimumProfessionalLicense(license) {
+			return model.NewAppError("", "license_error.feature_unavailable", nil, "feature is not available for the current license", http.StatusNotImplemented)
 		}
 		if !isPersistentNotificationsEnabled {
 			return priorityForbiddenErr