Update Charmhub home page (16)

[a-velasco]

This PR updates the metadata.yaml for PostgreSQL 16 releases on Charmhub in order to version the home page with the docs.

It addresses issue canonical/postgresql-operator#1082

Changes

• Replaced docs: link with new RTD docs - this new Charmhub feature will create a dedicated button in the sidebar.
• Updated summary: and description: keys, since they will be the new title and content of the Charmhub home page.
• Removed old broken link to chat.charmhub.io

Checklist

• I have added or updated any relevant documentation.
• I have cleaned any remaining cloud resources from my accounts.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 68.68%. Comparing base (f9f9d1f) to head (ab0d920).
⚠️ Report is 2 commits behind head on 16/edge.

❌ Your project status has failed because the head coverage (68.68%) is below the target coverage (70.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@           Coverage Diff            @@
##           16/edge    #1070   +/-   ##
========================================
  Coverage    68.68%   68.68%           
========================================
  Files           15       15           
  Lines         4043     4043           
  Branches       582      582           
========================================
  Hits          2777     2777           
  Misses        1058     1058           
  Partials       208      208           

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