Enable metadata assertion and chart lock generation

[komish]

• The owners module changes enables parsing Red Hat OWNERS files and asserting that metadata meets new expectations of the content.

• The packagemapping module provides hooks to generating chart locks based on the content of a given repository's charts/ directory.

• The pullrequest module changes facilitates asserting metadata given a pull request as an input.

• Entrypoints are then added to setup.cfg to simplify calling of this new logic in CI.

Depends on https://github.com/openshift-helm-charts/development/pull/313 for Python Style to pass.

[komish]

@mgoerens I believe I've addressed all of the issues that I've agreed should be addressed here. I've left things as individual commits here because we're making a lot of changes, and I wanted to make it a bit easier to track what change was motivated by which code review comment.