Bug Report: Externally managed vttablet fails to start with permissions error

[dbussink]

Overview of the Issue

In #14565 we added a check for the permissions, but this check also results in externally managed tablets to not start up. Those don't need the full permissions and in that case, permissions are the responsibility of the Vitess admin and we should run the guard.

Reproduction Steps

Start externally managed tablet and point it at MySQL without SUPER privileges.

Binary Version

Since https://github.com/vitessio/vitess/pull/14565

Operating System and Environment details

-

Log Fragments

No response