feat: add help text for sitemap_gen metadata fields

[Srishti-Gupta74]

Description

Added help text for all user-facing fields in plugins/sitemap_gen/metadata.json to improve clarity when configuring the sitemap_gen plugin.

Changes made:

• Added help text for the target field describing the expected URL input.
• Added help text for the depth field explaining its effect on sitemap generation.
• Refreshed the plugin checksum after updating the metadata.

Related Issues

Closes #531

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?

• Ran:

  python scripts/refresh_plugin_checksum.py --plugin sitemap_gen

• Verified the metadata changes using:

  git diff

• Confirmed the checksum was updated successfully and only the intended metadata fields were modified.

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.