Support for Virtual Threads

[csviri]

Fabric8 client should already support virtual threads, we should add a sample, in case improve our configuration API to support it more nicely.

Note that thread pools are already customizable, so might work just also now with virtual thread based thread pools.

Virtual threads will probably lead to more efficient threading and higher throughput.

[csviri]

I added a PR with a sample, in which the client and the reconciler executor is using virtual threads. We should also check if we should replace other thread pools in ExecutorServiceManager. We might want just to expose a simplified config param ( like withVirtualThreads(boolean) ) to make it easier usage for users.

We need also to:

• verify that reconciliation works properly and egfficiently
• We probably will have issues with ThreadLocals for that we will probably have to specifically handle source code for different Java versions

[csviri]

Note: we might want to target v5.7 with this if would take a long time to properly handle it.