docs: addition of a reactive pitfalls reference

[jponge]

This reference page is to be completed with our observations of how users might have incorrect assumptions on how to use Mutiny and reactive in general.

[cescoffier]

Awesome! We should definitely link this doc from the Quarkus doc

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.46%. Comparing base (6a2c6f0) to head (b466243).
Report is 14 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1546      +/-   ##
============================================
+ Coverage     89.44%   89.46%   +0.01%     
- Complexity     3271     3275       +4     
============================================
  Files           457      457              
  Lines         13274    13274              
  Branches       1644     1644              
============================================
+ Hits          11873    11875       +2     
+ Misses          788      784       -4     
- Partials        613      615       +2     

see 11 files with indirect coverage changes