Prepend [skip ci] to commit messages by default

[zackproser]

• Allow users to opt-out of this behavior via the new --no-skip-ci flag

Description

Fixes #88 .

TODOs

Read the Gruntwork contribution guidelines.

• [x] Update the docs.
• [x] Run the relevant tests successfully, including pre-commit checks.
• [x] Ensure any 3rd party code adheres with our license policy or delete this line if its not applicable.
• [x] Include release notes. If this PR is backward incompatible, include a migration guide.

Release Notes (draft)

Added / Removed / Updated [X].

Migration Guide

Starting with this release, git-xargs will automatically prepend [skip ci] to commit messages it authors, unless you pass the new flag --no-skip-ci to opt out of this behavior.

This change is intended to make git-xargs safer to use for large jobs that might otherwise lead to excessive continuous integration jobs that might also be costly.

If you use git-xargs in scripts or automated workflows and do not wish to have [skip ci] prepended to every commit message, be sure to pass the --no-skip-ci flag.

Alternatively, if you wish to use a different prefix other than [skip ci], you can write the string literal into your commit messages like so --commit-message [skip-azure] and then pass the --no-skip-ci flag.

[zackproser]

Thanks for review! Going to merge this in now.