Convert entry_points to dotted notation

[MHendricks]

Convert the entry point's _ separator to . to be inline with the group spec of https://packaging.python.org/en/latest/specifications/entry-points/#data-model. Keeping the underscore in hab_gui.

Checklist

• I have read the CONTRIBUTING.md document
• I formatted my changes with black
• I linted my changes with flake8
• I have added documentation regarding my changes where necessary
• Any pre-existing tests continue to pass
• Additional tests were made covering my changes

Types of Changes

• Bugfix (change that fixes an issue)
• New Feature (change that adds functionality)
• Documentation Update (if none of the other choices apply)

Proposed Changes