docs: Add Link (and redirect) to .NET docs

[lokitoth]

Pulls the .NET Docs a bit more into the documentation website proper:

• Add a link from the 0.4-series Python docs to
• Adds a transient redirect from /dotnet/ to /dotnet/dev/ to forward to the dev docs until we do a non "-dev" release

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.37%. Comparing base (ec314c5) to head (3f2a38d).
Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5534      +/-   ##
==========================================
+ Coverage   78.36%   78.37%   +0.01%     
==========================================
  Files         167      167              
  Lines        9933     9933              
==========================================
+ Hits         7784     7785       +1     
+ Misses       2149     2148       -1     

Flag	Coverage Δ
unittests	78.37% <ø> (+0.01%)	⬆️

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