Add a few default_help_reprs (#15588)
Add a few default_help_reprs (#15588)

Fixes #9412 (technically already fixed, but this wraps it up nicely).

Generated docs and ensured they look good.

[ci skip-rust]

pantsbuild/pants,benjyw/pants,pantsbuild/pants,pantsbuild/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,benjyw/pants,pantsbuild/pants,benjyw/pants,pantsbuild/pants