MM-11120 Adding setting to disable email invitations and rate limiting. (#9063)

* Adding setting to disable email invitations.

* Adding a setting and rate limiting for email invite sending.

* Modifying email rate limit to 20/user/hour

* Adding EnableEmailInvitations to client side config and command.

api4/team_test.go

@@ -1935,6 +1935,15 @@ func TestInviteUsersToTeam(t *testing.T) {
 	utils.DeleteMailBox(user1)
 	utils.DeleteMailBox(user2)
 
+	th.App.UpdateConfig(func(cfg *model.Config) { *cfg.ServiceSettings.EnableEmailInvitations = false })
+
+	_, resp := th.SystemAdminClient.InviteUsersToTeam(th.BasicTeam.Id, emailList)
+	if resp.Error == nil {
+		t.Fatal("Should be disabled")
+	}
+
+	th.App.UpdateConfig(func(cfg *model.Config) { *cfg.ServiceSettings.EnableEmailInvitations = true })
+
 	okMsg, resp := th.SystemAdminClient.InviteUsersToTeam(th.BasicTeam.Id, emailList)
 	CheckNoError(t, resp)
 	if !okMsg {