Per query resource allocation (i.e. evenly split memory and CPU between queries)

[rampage644]

At the moment it is possible to specify per-executor memory limits. Add support for another mode for resource allocation - per-query.

This will be the mode whereas both CPU and memory is going to be evenly divided for available concurrency. For CPU this can be either achieved via through target_partitions settings or limiting thread pool for DedicatedExecutor.