Docs Update: Add API endpoint for `personal_access_token` to return information about the PAT thats being used

Proposal

Currently the API has an endpoint for /personal_access_tokens which have the ability to:

• list personal access tokens
• get a single access token by id
• revoke a personal access token
• create a personal access token.

However a feature that I believe is missing, is the ability to pass a PAT into the API endpoint and for the API to return information about the PAT thats being used.

The API needs an endpoint exposed at /personal_access_token that runs this ruby code https://gitlab.com/gitlab-org/gitlab/-/blob/master/lib/api/entities/personal_access_token.rb and returns the access token details.

This would be very similar to the /user endpoint which returns the current user information based on the access token being used.

New endpoint:
GET /personal_access_token

Example request:

curl --header "PRIVATE-TOKEN: <your_access_token>" "https://gitlab.example.com/api/v4/personal_access_token"

Example response:

{
  "id": 4,
  "name": "Test Token",
  "revoked": false,
  "created_at": "2020-07-23T14:31:47.729Z",
  "scopes": [
      "api"
  ],
  "user_id": 24,
  "last_used_at": "2021-10-06T17:58:37.550Z",
  "active": true,
  "expires_at": null
}