refactor: make batcher configurable (backport #815)

[mergify[bot]]

This is an automatic backport of pull request #815 done by Mergify. Cherry-pick of 04208950a2f798ecba8757e5e77ed41ebc0fdf09 has failed:

On branch mergify/bp/release/v1.x.x/pr-815
Your branch is up to date with 'origin/release/v1.x.x'.

You are currently cherry-picking commit 0420895.
  (fix conflicts and run "git cherry-pick --continue")
  (use "git cherry-pick --skip" to skip this patch)
  (use "git cherry-pick --abort" to cancel the cherry-pick operation)

Changes to be committed:
    modified:   batch.go
    modified:   batch_test.go
    modified:   benchmarks/bench_test.go
    modified:   immutable_tree.go
    modified:   iterator_test.go
    modified:   mutable_tree.go
    modified:   mutable_tree_test.go
    modified:   nodedb.go
    modified:   nodedb_test.go
    modified:   options.go
    modified:   proof_iavl_test.go
    modified:   testutils_test.go
    modified:   tree_random_test.go
    modified:   tree_test.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
    both modified:   CHANGELOG.md

To fix up this pull request, you can check it out locally. See documentation: https://docs.github.com/en/github/collaborating-with-pull-requests/reviewing-changes-in-pull-requests/checking-out-pull-requests-locally

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