docs: expand documentation for sample_metadata()

[Tanisha127]

This PR expands the documentation for sample_metadata() to provide:

• A clearer summary of how metadata is assembled
• Detailed parameter descriptions
• An expanded description of the returned DataFrame
• Explanation of merged metadata sources (general metadata, QC metadata, surveillance flags, AIM, cohorts)

Fixes #553.

[Tanisha127]

Hi @jonbrenas and @ahernank,

I’ve opened PR #933 to expand the documentation for sample_metadata().
I’d appreciate your feedback when you have time.
Also, the workflows are awaiting maintainer approval for CI to run.

Thank you!

[Tanisha127]

Hi @jonbrenas ,
All checks are now passing for this PR. Could you please review it when convenient?
Happy to make any changes if needed.
Thank you!

[jonbrenas]

The "summary" and "returns" are good, the "parameters" are read from base_params and are thus already described elsewhere, so they are not needed here.

[Tanisha127]

Hi @jonbrenas, I've removed the parameters section as requested — only summary and returns remain. Could you please take another look when convenient? Thank you!