Merge plugin supports checking the PR content after /merge command

[Mini256]

Feature Request

• I have searched the issues of this repository and believe that this is not a duplicate.

Is your feature request related to a Issue or PR(Optional)

• Which project: TiKV

• PR or Issue Link: new PR requirement and commit message proposal tikv/community#162 (comment)

Describe the feature you'd like:

In the current merge plugin, when the config item store_tree_hash is enabled, the merge plugin will temporarily save the last commit SHA value while the /merge command triggers. When there is a new commit be submitted, the plugin checks whether the last commit (except the commit of merge-base) SHA changes. If changed, the robot will remove the status/can-merge label on pull request.

In some cases, we want to ensure that some contents in PR other than code will not change during the process from /merge to PR being merged. If changed, PR should be canceled merging.

Do you have any ideas on how to implement it? (Optional)

1. Add store_verify_payload_hash and verify_payload_template options
2. In the verify_payload_template option, we can use the syntax of Go Template to define what we need to verify, for example:

ti-community-merge:
  - repos:
      - tikv/tikv
      - tikv/pd
    store_tree_hash: true
    store_verify_payload_hash: true
    verify_payload_template: |
       {{- .ExtractContent "(?im)^Issue Number:(?P<content>.+)" .Body -}}
       {{- .ExtractContent "(?i)\x60\x60\x60commit-message(?P<content>[\\w|\\W]+)\x60\x60\x60" .Body -}}

3. When the /merge command trigger, the merge plugin will extract the content according to the verify_payload_template option as payload, then get the SHA value of payload and temporarily store it.
4. When the PR occurs edited event, if the bot found that the payload SHA has changed, it will remove the status/can-merge label from PR.

[ti-chi-bot]

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[ti-chi-bot]

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