Update repo search endpoint to search for specific repos instead of filtering all of them

• Fix the repo endpoint to actually return results for GitLab results. It would always get filtered out before because it filtered on full_name which is GitHub specific
• Updates the repo search endpoint to be more performant.
  • For GitLab, we use the search query parameter to fetch only what we need
  • For GitHub, we still have to fetch all and filter on our side

Fix https://gitlab.com/gitlab-org/gitter/webapp/-/issues/2472

Dev notes

• https://docs.gitlab.com/ee/api/projects.html#list-all-projects
• https://developer.github.com/v3/repos/#list-repositories-for-a-user
• https://developer.github.com/v3/search/#search-repositories

Testing strategy

This is best tested if you run through https://gitlab.com/gitlab-org/gitter/webapp/-/merge_requests/1823 instead

Todo

• Merge https://gitlab.com/gitlab-org/gitter/webapp/-/merge_requests/1823 (not a blocker but they go together)