Rename wb-manager add --uncompress-wacz to --unpack-wacz and add docs

[tw4l]

Description

1. Renames the new wb-manager add --uncompress-wacz option to --unpack-wacz.
2. Add documentation as well as CLI help text for new flag.

Related to #799

Motivation and Context

The new flag name is both more accurate and easier to type.

Also, existing features should be documented, especially if people are likely to use them!

Screenshots (if appropriate):

Types of changes

• Replay fix (fixes a replay specific issue)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Renaming of existing feature prior to first release it's included in

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added or updated tests to cover my changes.
• All new and existing tests passed.