Limit maximum Snapshot Parallel Workers user can create

[jgao54]

Set a more reasonable upper bound for Snapshot Parallel Workers value, the current maximum is max uint32. Locally testing with setting parallelism to the maximum value results in initial load to hang. We should propose a reasonable upper bound, or show a warning to user to that this value depends on the available cpus to be effective.

[iamKunalGupta]

maybe 4x/8x number of cores?
But should be overridable via the UI maybe via dynamicconf