Add Project Access Tokens to credentials inventory

What does this MR do and why?

• Adds project access tokens to the admin credentials inventory.
• Updates documentation and associated screenshot.

Screenshots or screen recordings

How to set up and validate locally

• Create a bunch of project access tokens on multiple project.
• As an instance adminstrator, look at the project access tokens in the Credentials Inventory and make sure that the data is correct.
• Attempt to revoke project access tokens.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.

Related to #243833 (closed)