Include the name of the repo in the filename for Bitbucket Server archives

When running a Bitbucket Server migration, the archive from the Bitbucket Server instance is stored in the `bbs_archive_downloads` directory. At the moment, the filename only contains the migration ID.

This makes it hard to identify which file is which, which makes life difficult when we want to ask a customer for a copy of their archive for debugging purposes.

We should include the name of the repo in the filename alongside the ID.

I started implementing this in https://github.com/github/gh-gei/pull/817, but it isn't fully done. It requires some reworking of the code, as currently the file on the Bitbucket Server and the filename we use for the CLI are the same, which will no longer be the case.

## Todo
- [ ] When downloading and write the archive to the disk, use `{bbs-project-name}-{bbs-repo-name}-{export-archvie-job-id}` naming format for the archive name.