feat: introduce batching mode

[dora-gt]

Thinking of this change.

Introduce BatchingMode which enables users to expressly specify the timing of executing the batched operations.

Feedbacks welcome.

[apollo-cla]

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[dora-gt]

I'd like this PR to be merged, what do you think? Do you guys think this is not necessary or should I do something?

It just adds functionality, not breaking anything. Users can now control when to execute batches.

[dora-gt]

ping @hwillson @benjamn