Gitaly is in the process of adding the ability to rewrite repository
history. To do this, we will use `git-filter-repo`, built by a
prominent contributer to the Git project. The script becomes available
as a Git subcommand when it is placed in $PATH.

Unfortunately, this tool is written in Python, so we are forced to
introduce a fairly heavy dependency into the Gitaly images.

We install it via `pip3` for both ubi and Debian images to ensure we
have a consistent version in all of our containers. This writes a
wrapper script to `/usr/local/bin`.

Changelog: added