WIP: Resolve "Add Last Activity for Personal Access Tokens"

What does this MR do?

Currently there's no way to identify whether a personal access token is in use, or when it was last used. This makes it difficult to efficiently maintain GitLab as a service.

1. Adds a last_used_at attribute to Personal Access Tokens
2. Update a token's last_used_at whenever it gets used
3. Display how long ago a personal access token was last used

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team

Closes #33162 (closed)