feat: Adding Github action to check CC's CDX index server every week

[malteos]

This PR adds a Github action that runs a check of the CC CDX index server every week.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 95.78%. Comparing base (b6f5f02) to head (09719e1).
⚠️ Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #60   +/-   ##
=======================================
  Coverage   95.78%   95.78%           
=======================================
  Files           7        7           
  Lines         877      877           
=======================================
  Hits          840      840           
  Misses         37       37           

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[wumpus]

This is more than I expected -- checking the rate limiting -- but let's see if it works out!