Import improvements

What does this MR do?

This import adds support for repositories with 400k-800k github issue comments, and also improves logging such that users can see what is going on when they run an import on the cli.

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

I'm sure there are ways to improve the logging output, as well as when we switch from parallel to sequential imports. In my case, the sequential import was a much nicer experience for debugging on the cli.

Why was this MR needed?

We had no way to know why an import failed, nor were we able to import github repositories with many comments.

Screenshots (if relevant)

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
• Internationalization required/considered
• End-to-end tests pass (package-and-qa manual pipeline job)

What are the relevant issue numbers?

#39254 (moved)