Upgrade doorkeeper-openid_connect

What does this MR do?

Upgrades doorkeeper-openid_connect and supporting gems, and renames the jws_private_key secret to openid_connect_signing_key

Are there points in the code the reviewer needs to double check?

Needs to be coordinated with https://gitlab.com/gitlab-org/omnibus-gitlab/merge_requests/1943

The reason for renaming the secret was https://gitlab.com/gitlab-com/infrastructure/issues/2259

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Documentation created/updated
• API support added
• Tests added for this feature/bug
• Review
  • Has been reviewed by UX
  • Has been reviewed by Frontend
  • Has been reviewed by Backend
  • Has been reviewed by Database
• Conform by the merge request performance guides
• Conform by the style guides
• Squashed related commits together

What are the relevant issue numbers?