Api for project access token

What does this MR do?

This MR adds index, create and revoke api for Project Access Token (referenced to as PrAT hereon). The APIs will be used in the FE page to create Project Access Tokens: !30214 (diffs)

Action	Functionality
index	List active and inactive access tokens and available scopes. It also makes available the newly created PrAT (if applicable).
create	Creates and returns PrAT. It internally invokes the CreateAccessToken service. For details, ref: !28621 (merged)
revoke	Revokes access token, Removes maintainer access for the Project Bot, Transfer issuables to ghost user

Refactor changes

For better readability, Resources::CreateAccessTokenService has been updated to ResourceAccessTokens::CreateService.

Feature availability

This feature is behind the feature flag: resource_access_token and is not applicable for Gitlab.com until #15666 (closed) is resolved.

Mentions #210057 (closed)

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