[BB Importer] Save the error trace and the whole raw document

What does this MR do?

This will help us to debug problems like this https://gitlab.com/gitlab-org/gitlab-ce/issues/27476

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

I don't think so

Why was this MR needed?

To make debug problem easier.

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

https://gitlab.com/gitlab-org/gitlab-ce/issues/27476