Allow specfiying agent uuids for bulk group add

[paulewog]

Description

This allows specifying Agent UUIDs instead of numeric IDs for bulk group addition.

Fixes #607

Type of change

Please delete options that are not relevant.

• [x] New feature (non-breaking change which adds functionality)
• [ ] This change requires a documentation update

How Has This Been Tested?

• [x] Tested single id
• [x] Tested single uuid
• [x] Tested multiple ids
• [x] Tested multiple uuids
• [x] Tested mix of id and uuid (fails)

Test Configuration:

• Python Version(s) Tested: 3.9.7
• Tenable.sc version (if necessary): N/A

Checklist:

• [ ] My code follows the style guidelines of this project
• [x] I have performed a self-review of my own code
• [x] I have commented my code, particularly in hard-to-understand areas
• [ ] I have made corresponding changes to the documentation
• [ ] My changes generate no new warnings
• [ ] I have added tests that prove my fix is effective or that my feature works
• [x] New and existing unit tests pass locally with my changes
• [x] Any dependent changes have been merged and published in downstream modules