Add support for .git-blame-ignore-revs files

[thehale]

Some repositories contain a file listing commits to ignore for git blame operations. That file can be passed to the git blame command using the --ignore-revs-file option available in Git v2.23 or later. Most repositories name this file .git-blame-ignore-revs and locate it at the root of the repository.

It would be great if git-authorship supported looking for this file with its default name and location when computing authorship. Once a CLI is added, a CLI option for the file path should also be provided to support unconventional blame ignore files.

[thehale]

A nice article explaining the rationale behind ignoring some commits from git blame: https://moxio.com/blog/ignoring-bulk-change-commits-with-git-blame/