api,coordinator: add drain API orchestration#4762

hongyunyan wants to merge 3 commits intosplit/pr-4190-2c-coordinator-drain-runtimepingcap/ticdc:split/pr-4190-2c-coordinator-drain-runtimefrom

split/pr-4190-3-drain-api-rebasedpingcap/ticdc:split/pr-4190-3-drain-api-rebasedCopy head branch name to clipboard