Align the Uni::eventually operators to onTermination() semantics

[jponge]

The Uni::eventually(Runnable) operator had been previously moved from onItemOrFailure() to onTermination() semantics so as to handle cancellation on top of already handling items and failures.

This aligns the eventually(Supplier<Uni<T>>) variant with its eventually(Runnable) counterpart.

Fixes #1742.

BREAKING CHANGE: this may break code bases where onItemOrFailure() semantics were correctly assumed and cancellation was handled separately.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 89.50%. Comparing base (ba0cf7d) to head (54a161d).
Report is 7 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #1743      +/-   ##
============================================
+ Coverage     89.26%   89.50%   +0.24%     
- Complexity     3275     3288      +13     
============================================
  Files           458      458              
  Lines         13365    13365              
  Branches       1651     1651              
============================================
+ Hits          11930    11963      +33     
+ Misses          807      787      -20     
+ Partials        628      615      -13     

Files with missing lines	Coverage Δ
...entation/src/main/java/io/smallrye/mutiny/Uni.java	90.90% <100.00%> (ø)

... and 13 files with indirect coverage changes

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