WIP: Federation Enhancements: Identity Model

What does this MR do?

This MR is the first of several for federation enhancements to GitLab. Please see #33665 (closed) for a detailed description. This MR in particular covers the base updates to the identity model. Per the auth hash schema, credentials (token, expires, and expires_at) are being added to entries in the identities table. The OmniAuth identity linker base is also being enhanced to reflect that identities which expire can be updated. Finally, minor additions included are updating the jwt gem to return credentials from the auth hash, as well as updating the accesses to the auth hash data itself via instance variables.

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance 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

Security

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