rowexec/colexec: add cumulative contention time to EXPLAIN ANALYZE #56612
Description
Actual contention events will be implemented in #55583, but in the meantime we can introduce a testing cluster setting that will produce mock contention events that follow the same structure as that defined by the issue.
This issue also tracks building the SQL execution infrastructure around those contention events. To start with, we'll want to surface how much contention happened in any operators that use disk. This should be a sum of the duration of each contention event.