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

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

server/channels/app/notification.go

@@ -1465,7 +1465,7 @@ func (a *App) allowChannelMentions(c request.CTX, post *model.Post, numProfiles
 
 // allowGroupMentions returns whether or not the group mentions are allowed for the given post.
 func (a *App) allowGroupMentions(c request.CTX, post *model.Post) bool {
-	if license := a.Srv().License(); license == nil || (license.SkuShortName != model.LicenseShortSkuProfessional && license.SkuShortName != model.LicenseShortSkuEnterprise) {
+	if !model.MinimumProfessionalLicense(a.Srv().License()) {
 		return false
 	}