Resolve "Show detailed status for GitHub Importer"

What does this MR do and why?

This MR implements detailed github status, as described in #348744 (closed)

Screenshots or screen recordings

New_Project___GitLab__1_

Speed-up video (full import takes ~30 minutes): https://www.youtube.com/watch?v=DrNb7Nw6Q9Q

How to set up and validate locally

1. Fork some "big enough" repository to your GitHub (I was using https://github.com/vuejs/test-utils as source, take 30 min to complete importing this repo)
2. Generate GitHub PAT token
3. Open /projects/new#import_project
4. Select GitHub import and use your GitHub PAT token
5. Start importing repository, observe behavior

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.