Add configuration option to enable/disalbe `CoalesceBatchesExec`

[andygrove]

Is your feature request related to a problem or challenge? Please describe what you are trying to do.
I would like to be able to use configuration options to control whether CoalesceBatchesExec operators are inserted into the plan and also to control the target batch size.

Describe the solution you'd like
☝️

Describe alternatives you've considered
None

Additional context
None