[CLD-6894] Add 60, 30, and 7 day reminder emails for Cloud Renewals (#25883)

* Add email notifications for Cloud Renewals

* Updates

* Updates

* Update app-layers

* make build-templates

* Add ability to set an env variable as a unix timestamp in s as the current date when getting DaysToExpiration

* Add a mechanism to ensure at least one admin receives every email

---------

Co-authored-by: Mattermost Build <build@mattermost.com>
Co-authored-by: Gabe Jackson <3694686+gabrieljackson@users.noreply.github.com>

server/channels/app/server.go

@@ -1415,7 +1415,8 @@ func (s *Server) doLicenseExpirationCheck() {
 	}
 
 	if license.IsCloud() {
-		mlog.Debug("Skipping license expiration check for Cloud")
+		appInstance := New(ServerConnector(s.Channels()))
+		appInstance.DoSubscriptionRenewalCheck()
 		return
 	}