Add after_transaction_batch hook

[yujonglee]

Is your feature request related to a problem? Please describe.

Currently, after_batch runs inside transaction. There's nothing I can do if I want to do some extra work after batch outside of transation.

Describe the solution you'd like

Add after_transaction_batch hook

Describe alternatives you've considered

Use after_transaction for individual changeset.

[zachdaniel]

I've labeled this as "good first issue", but it is actually reasonably complex. Its more like a "good second" or "good third" issue 😆 But its a digestible piece to add and would be very useful :)

[zachdaniel]

Closing as a duplicate of #1580 (that one refers to both before and after batch hooks)