Simplify re-running on repos that failed

**Describe the solution you'd like**

Optionally write all the failed to update repos to a .txt file in the format that `git-xargs --repos` accepts.

**Describe alternatives you've considered**

In the process of updating about 2500 repos I ran into multiple errors and had to re-run git-xargs multiple times, and the process looked like this:

1) run git-xargs redirecting stdout / stderr to a file
2) copy the tables following text like "Repos whose initial Pull Request failed to be created due to GitHub rate limits" or "Repos that were unable to be cloned to the local filesystem" etc. to a txt file
3) run a vim macro to remove the table formatting (e.g. `------`) so that it is in a format that `git-xargs --repos` can accept
4) re-run git-xargs with `--repos` arg pointing to that manually created file, and repeat steps 1-4 until all repos successfully processed or intentionally skipped

Ideally there wouldn't be any errors, but with so many repos that might be impractical, and the errors could also be user-error based on the command passed to git-xargs. A more efficient user experience might be the following:

a) run git-xargs redirecting stdout / stderr to a file and the option `--failed-repo-output-file /tmp/failed_to_update_repos.txt`
b) review stdout / stderr and remove any repos from ` /tmp/failed_to_update_repos.txt` that you intentionally don't want to retry
c) run git-xargs with `--repos /tmp/failed_to_update_repos.txt` and `--failed-repo-output-file /tmp/failed_to_update_repos2.txt` etc. (and it might be good to support `--repos` and `--failed-repo-output-file` pointing to the same file)