runners: add explanation for updating profile::gitlab::trusted_runner_id_regex
In Ifb4930cb9918f3b56c1df7aacbf993795f3e6a40 a Nginx config was introduced which uses the Trusted Runner IDs. This IDs have to be updated in case the Trusted Runner tokens are rotated. So this change adds a little help text to the output.
Bug: T366786