[MM-31497] - Prevent end users from inviting people and exceeding the free tier limits (#16786)

* [MM-31497] - Prevent end users from inviting people and exceeding the free tier limits

* Update error

* Commit forgotten code

* Chnage impl-1

* Change impl-2

* Remove test

* Include tier status

* Renable permissions check

* Change endpoint name

* Update endpoint

* Update api4/cloud.go

Co-authored-by: Maria A Nunez <maria.nunez@mattermost.com>

* Add test for new endpoint

* Format code

Co-authored-by: Mattermod <mattermod@users.noreply.github.com>
Co-authored-by: Maria A Nunez <maria.nunez@mattermost.com>

model/cloud.go

@@ -128,3 +128,8 @@ type FailedPayment struct {
 	LastFour       int    `json:"last_four"`
 	FailureMessage string `json:"failure_message"`
 }
+
+type SubscriptionStats struct {
+	RemainingSeats int    `json:"remaining_seats"`
+	IsPaidTier     string `json:"is_paid_tier"`
+}