Docs: Adds docs for hosts to remove the ability of participants to hide submissions

[aditi-dsi]

This PR adds docs to explain how challenge hosts can lock submission visibility such that participants cannot hide their submissions and all submissions are strictly public.

fixes #4756

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.94%. Comparing base (96968d6) to head (bcef283).
⚠️ Report is 1234 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #4767      +/-   ##
==========================================
+ Coverage   72.93%   76.94%   +4.00%     
==========================================
  Files          83       21      -62     
  Lines        5368     3608    -1760     
==========================================
- Hits         3915     2776    -1139     
+ Misses       1453      832     -621     

see 75 files with indirect coverage changes
see 75 files with indirect coverage changes

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