Implement flag "skip-push", deprecate flag "push"

[rosshamish]

• Implements a new input flag skip-push, default false. If true, skips pushing any commit or tag created during the version bump.
• Deprecates the input flag push, which was documented as skipping the push, but whose actual behavior is to skip all operations (version bump in package.json, git commit, git tag, git push). In a future major version, this flag could be renamed to no-op, or even just removed since its behavior can be achieved using the if: conditionals in Github Actions anyway.

Tested using the end-to-end test suite (needed some modifications before it would run), over here: https://github.com/rosshamish/gh-action-bump-version/pull/1/checks

[phips28]

thx 🙂

I never used the test suite, as it never worked for me 🙈