docs: clarify crawl discovery plugin boundaries

[Vishvadharman]

Description

Clarifies the overlap between the crawl/discovery plugin family by documenting the purpose and boundaries of crawler, katana, spider, and sitemap_gen.

Changes include:

• Updated plugin metadata descriptions to better reflect actual execution behavior
• Clarified the differences between the four Katana-based discovery plugins
• Added documentation describing intended use cases and execution differences
• Updated catalog descriptions to reduce ambiguity for users
• Documented that no plugins were renamed or merged as part of this change

Related Issues

Closes #544

Type of Change

• 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 not work as expected)
• Documentation update

How Has This Been Tested?

• Reviewed plugin metadata for crawler, katana, spider, and sitemap_gen
• Verified descriptions align with command templates and execution behavior
• Confirmed documentation accurately reflects plugin boundaries and intended usage

Checklist

• My code follows the code style of this project.
• I have performed a self-review of my own code.
• 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.