Support for pre/post commit hooks

[malnvenshorn]

Closes #178

Implements two new command line parameter --pre-commit-hook, --post-commit-hook and their config counterparts pre_commit_hook, post_commit_hook.

• Paths must bei either absolute or relative to the working directory.
• If a hook exits with a return_code != 0 bumpver will stop any further execution
• Two environment variables are set for the scripts: BUMPVER_OLD_VERSION, BUMPVER_NEW_VERSION
• Any output (stdout, stderr) will be piped to the bumpver log

Example output:

$ bumpver update --post-commit-hook changelog.sh
INFO    - fetching tags from remote (to turn off use: -n / --no-fetch)
INFO    - Old Version: 2023.1001-alpha
INFO    - New Version: 2023.1002-alpha
INFO    - git commit --message 'bump version 2023.1001-alpha -> 2023.1002-alpha'
INFO    - Run post-commit hook: changelog.sh
INFO    -   Adding new item in CHANGES.md
INFO    -   Commiting CHANGES.md
INFO    - git tag --annotate 2023.1002-alpha --message '2023.1002-alpha'

$bumpver update --post-commit-hook changelog.sh
INFO    - fetching tags from remote (to turn off use: -n / --no-fetch)
INFO    - Latest version from VCS tag: 2023.1002-alpha 
INFO    - Working dir version        : 2023.1002-alpha
INFO    - Old Version: 2023.1002-alpha
INFO    - New Version: 2023.1003-alpha
INFO    - git commit --message 'bump version 2023.1002-alpha -> 2023.1003-alpha'
INFO    - Run post-commit hook: changelog.sh
ERROR   -   Environment variable FOOBAR is missing
ERROR   - Script exited with an error. Stopping

Checklist

• [x] Add tests
• [x] Run: make fmt lint mypy test test_compat
• [x] Update documentation

[mbarkhau]

Great work, thank you!