Ports omniauth-jwt gem onto GitLab OmniAuth Strategies suite

What does this MR do?

Ports https://github.com/mbleigh/omniauth-jwt onto the GitLab OmniAuth::Strategies suite

Why was this MR needed?

The gem was not actively being developed and we were being affected by a long lasting bug More information can be found in the following links:

• https://gitlab.com/gitlab-org/gitlab-ce/issues/45727
• https://github.com/mbleigh/omniauth-jwt/issues/2
• https://github.com/mbleigh/omniauth-jwt/pull/5

Screenshots

• If there is no account connected to that JWT account in GitLab

• If there is an account connected to that JWT account in GitLab

  • You can connect an account in Settings > Account

- Sign up successfully

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• Review
  • Has been reviewed by Backend
• Conform by the merge request performance guides
• Conform by the style guides

What are the relevant issue numbers?

Closes 45727