add docs on CI workflow inputs

[jameslamb]

Contributes to rapidsai/shared-workflows#376

• adds descriptions for all inputs to workflows triggered by workflow_dispatch

Description

I'd missed cuopt in rapidsai/shared-workflows#376, and also want to pull these changes off of #359 to shrink the diff there.

Issue

Helps with #122 (via making #359 a bit easier to review)

Checklist

• I am familiar with the Contributing Guidelines.
• Testing
  • New or existing tests cover these changes
  • Added tests
  • Created an issue to follow-up
  • NA
• Documentation
  • The documentation is up to date with these changes
  • Added new documentation
  • NA

[jameslamb]

/merge