feat: split extras by features

[aslafy-z]

Follow up #95 that was reverted at 6fa86f4

Fixes #44

Test with

pip install -e git+https://github.com/adobe/himl.git@refs/pull/144/head#egg=himl
pip install -e git+https://github.com/adobe/himl.git@refs/pull/144/head#egg=himl[vault]
pip install -e git+https://github.com/adobe/himl.git@refs/pull/144/head#egg=himl[s3]
pip install -e git+https://github.com/adobe/himl.git@refs/pull/144/head#egg=himl[all]

[aslafy-z]

@amuraru Hey, can you please give a look? I would love to use to project without pulling 90% libraries I don't need. Thank you!