This change allows to add fixup commits by running the command
`git commit --fixup=<sha>` without complaining about the commit
message not being in conventional commit format. (Running the
git command will result in the commit title of the referenced
commit with `fixup!` prepended. It will later be squashed with
the referenced commit in a git rebase.)
This change allows a different project to override the definitions
by providing a local `commit-msg-defs` file while still sharing the
`commit-msg` hook. Other projects might have a different set of
scopes.
Adds support for conventional commit style validation of all commit
messages and makes configuration against all Keyman repos
straightforward with the configure-repo.sh script.
