Allow admins to list PAT tokens via REST API

Problem solve

In #36742 (closed) we implemented a credentials inventory to enable administrators to list user access credentials, including Personal Access Token (PAT) records.

An HTML UI does not sufficiently support larger organizations that rely on GitLab's APIs to programmatically carry out many functions within the application.

Further details

Although GitLab is "GraphQL first", this feature is expected to be used in conjunction with the REST API for ApplicationSetting and should be implemented in the REST API on that basis.

Intended users

• Sidney (Systems Administrator)
• Cameron (Compliance Manager)

Proposal

Add a REST endpoint that allows an administrator to list all user Personal Access Token (PAT) records.