rpc: improve security posture of debug zip user

We have a created role `debug_user` to collect debug zips. The user needs to be manually created and managed by the cluster administrator. This improves the current security status quo of having to always have a root user to manage the cluster and makes the cockroachdb cluster compliant to security standards since the `debug_user` can be disabled by dropping the user associated with the role.

After some discussions with @cthumuluru-crdb and @aa-joshi, we came to the conclusion that the security posture can be further improved by having a whitelisting for the admin and status endpoints which are only needed for debug zip service. The complete list can be found [here](https://docs.google.com/document/d/1fPsIqLPbhmXtHOnPH5KH5YQhxBz_1QWI_nVFXslBCg0/edit?tab=t.0#heading=h.ku4tvtfr2xtj). This will allow us to have gated access to RPCs and further improve the debug zip service.

Jira issue: CRDB-57473

Start with the debug zip service and the admin and status endpoints listed in the linked design document. Trace how the debug_user role is created and used, then establish the gated RPC scope and verify that debug zip collection works without a root user and that the associated user can be disabled.

Written by the indexing model from the issue text.