Improve performance of GitHub importer

Merged Douglas Barbosa Alexandre requested to merge fix-github-importer-slowness into master

What does this MR do?

  • Fetch all refs in a single run
  • Skip merge request metrics

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

This is based upon !9992 (merged) and depends on gitlab-shell!125 (merged). After the first gets merged I will rebase this one.

Why was this MR needed?

The GitHub import process is extremely slow for large repositories.

Does this MR meet the acceptance criteria?

What are the relevant issue numbers?


@smcgivern @rspeicher @brodock @jameslopez