Blocking improvements max-concurrency

[ozangunalp]

Draft PR for discussions

Currently, Reactive Messaging controls the @Blocking method max concurrency level using the pool size attribute of the vertx worker pool created for the blocking execution.

However, there is a second aspect that affects the max concurrency which is the mutiny concurrency level when merging multiple Uni's into a Multi: https://smallrye.io/smallrye-mutiny/2.3.1/tutorials/transforming-items-asynchronously/#transforming-items-from-multi-the-merge-vs-concatenate-dilemma

This last control how many items will be requested upstream in parallel and effective only when blocking with ordered=false.

This PR changes how the Mutiny merge concurrency is configured :

• When available the max-concurrency is used to configure the Mutiny merge concurrency.
• If not it falls back to the current default value of Queues.BUFFER_S.

[ozangunalp]

Fixes #2198 and related to #2196

[codecov-commenter]

Codecov Report

Merging #2219 (4272ee0) into main (8fcdb37) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 4272ee0 differs from pull request most recent head d02a5a5. Consider uploading reports for the commit d02a5a5 to get more accurate results

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #2219      +/-   ##
============================================
- Coverage     77.72%   77.72%   -0.01%     
- Complexity     3695     3737      +42     
============================================
  Files           301      311      +10     
  Lines         12307    12458     +151     
  Branches       1570     1580      +10     
============================================
+ Hits           9566     9683     +117     
- Misses         2024     2053      +29     
- Partials        717      722       +5     

Impacted Files	Coverage Δ
...aging/providers/connectors/WorkerPoolRegistry.java	88.73% <ø> (ø)
...reactive/messaging/providers/AbstractMediator.java	82.72% <100.00%> (+0.48%)	⬆️
...eactive/messaging/providers/ProcessorMediator.java	93.14% <100.00%> (+0.05%)	⬆️
...eactive/messaging/providers/PublisherMediator.java	81.05% <100.00%> (ø)
...active/messaging/providers/SubscriberMediator.java	83.55% <100.00%> (+0.10%)	⬆️
...messaging/providers/extension/MediatorManager.java	84.53% <100.00%> (+1.58%)	⬆️

... and 19 files with indirect coverage changes

[ozangunalp]

@cescoffier simplified this PR to use max-concurrency value as mutiny merge concurrency.