MM-47228 - restrict guest invitation flow if subscription plan does n… (#21195)

* MM-47228 - restrict guest invitation flow if subscription plan does not support it

* fix i18n texts and add unit test

* test the scenario where guest invites are blocked by subscription

* cover the success scenarios for cloud free trial and paid subscription

* fix go vet

* use the cloud prefix for the sku

* fix unit tests

* check the licence value to determine if the guest accounts are enabled

* remove unnecessary changes for getting the subscription information

* restrict user demotion if guestAccounts is not available in license

Co-authored-by: Pablo Velez Vidal <pablo.velez@mattermost.com>

api4/user.go

@@ -2699,6 +2699,13 @@ func demoteUserToGuest(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
+	guestEnabled := c.App.Channels().License() != nil && *c.App.Channels().License().Features.GuestAccounts
+
+	if !guestEnabled {
+		c.Err = model.NewAppError("Api4.demoteUserToGuest", "api.team.invite_guests_to_channels.disabled.error", nil, "", http.StatusForbidden)
+		return
+	}
+
 	auditRec := c.MakeAuditRecord("demoteUserToGuest", audit.Fail)
 	auditRec.AddEventParameter("user_id", c.Params.UserId)
 	defer c.LogAuditRec(auditRec)