Add marker component for hidden entities that wasn't despawned

[Shatur]

It works, but:

• Docs need improvements.
• Not sure about the component name.
• The logic in server.rs is a bit on a dirty side, I need to clean it.

[codecov]

Codecov Report

❌ Patch coverage is 89.06250% with 7 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.71%. Comparing base (c5e2894) to head (233ecb5).
⚠️ Report is 2 commits behind head on master.

Files with missing lines	Patch %	Lines
src/server/replication_messages/updates.rs	78.94%	4 Missing ⚠️
src/client.rs	86.66%	2 Missing ⚠️
src/server.rs	96.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #741      +/-   ##
==========================================
- Coverage   90.75%   90.71%   -0.04%     
==========================================
  Files          72       72              
  Lines        4391     4461      +70     
==========================================
+ Hits         3985     4047      +62     
- Misses        406      414       +8     

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