Project Access Tokens - Delete project bot after token expires

What does this MR do?

Previously, a project bot user (created when Project Access Token is created) was not deleted or removed from project members when the access token expired. In MR !43605 (merged), project bot user membership is removed when the project access token expires. We also want to fully delete the user to avoid pressurizing the Users table with expired bots.

This MR adds logic to RemoveExpiredMembersWorker to check if the expired member is a project bot, then uses Users::DestroyService to delete them if they are a project bot.

Screenshots (strongly suggested)

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

Related to #267191 (closed)