Need a command for retry /merge but do not run all tests again

[you06]

This command would be /merge-without-tests which should be used after the committer re-trigger some failed tests.

• If the all tests haven't been triggered yet for the current commit, this command should equal to /merge
• If there are new commits, should restart all the tests.

[0xPoe]

@you06 Can I working on this?

[you06]

@Rustin-Liu Sure, thanks for it, but you may start this work after #35 get merged.