Move blocking random key generation to executor thread

[Arooba-git]

Thank you for the effort for this handy project!

This is a minor fix pertaining to a blocking call in KeyCommandsTests class as detected by BlockHound:

Of course the method is just used in the test cases but since this is the official examples repository, I think the fix could set a good example for how we should try to avoid blocking calls in reactive apps wherever possible, to keep the pipeline reactive end to end. :)

We re-ran the test cases and also evaluated the performance (in terms of latency) before and after the fix

Parking duration of main thread before fix

After