Avoid virtual thread pinning in RestClientsConfig

[mariofusco]

This is a fix for the virtual thread pinning problem reported here.

As reported by @radcortez here the more structural fix there would be removing the implicit CDI dependency thus completely getting rid of the ConcurrentHashMap. However, as he also confirmed, a rewriting of the REST Client configuration could take a while, so I followed @franz1981's suggestion and fixed at least the symptom simply avoiding to call the computeIfAbsent method from a virtual thread.

[franz1981]

I would avoid creating a new class (which implies a new class loaded) and using a single lock for all of them (even if virtual)...
given that the stack trace reported by the user is performing some blocking/long running operation, it means that using a single lock will serialize all of the them regardless what the "good" CHM concurrency allow...
Why not using a CompletableFuture value instead without caring if the caller is a virtual one?
It will reuse CHM and won't serialize the computes...

[mariofusco]

Why not using a CompletableFuture value instead without caring if the caller is a virtual one? It will reuse CHM and won't serialize the computes...

Do you mean having a ConcurrentHashMap<String, CompletableFuture<RestClientConfig>> ?

[franz1981]

Yep, clearly it would add some cost in term of footprint to everyone (non virtual threads), but there won't be any other adverse effects

[mariofusco]

Made obsolete and unnecessary by 4f31e0d