Add fine-grained control of time (backport #88)

[mergify]

This is an automatic backport of pull request #88 done by Mergify.
Cherry-pick of 7edb4c1 has failed:

On branch mergify/bp/v0.38.x/pr-88
Your branch is up to date with 'origin/v0.38.x'.

You are currently cherry-picking commit 7edb4c1.
  (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:   .gitignore
	deleted:    Dockerfile-test
	new file:   Dockerfile.test
	modified:   Makefile
	modified:   README.md
	modified:   cometmock/abci_client/client.go
	new file:   cometmock/abci_client/time_handler.go
	modified:   cometmock/main.go
	modified:   cometmock/rpc_server/routes.go
	new file:   cometmock/utils/txs.go
	new file:   e2e-tests/.gitignore
	new file:   e2e-tests/local-testnet-singlechain-restart.sh
	new file:   e2e-tests/local-testnet-singlechain-setup.sh
	new file:   e2e-tests/local-testnet-singlechain-start.sh
	new file:   e2e-tests/test_utils.go

Unmerged paths:
  (use "git add <file>..." to mark resolution)
	both modified:   e2e-tests/local-testnet-singlechain.sh
	both modified:   e2e-tests/main_test.go

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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