Add ciflow-bot implementation

[zhouzhuojie]

Stack from ghstack:

• -> #40

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Implementation logic

The implementation can be summarized as the following:

0. It has a kill switch, so that we can safely redeploy the lambda just in case something went wrong. It also has a list of rollout_users (currently just zhouzhuojie) that are enabled as an allowlist and will only run the bot for this group at the beginning of the rollout.

1. We are going to handle the following events.

  main(): void {
    this.app.on('pull_request.opened', this.handler.bind(this));
    this.app.on('pull_request.reopened', this.handler.bind(this));
    this.app.on('pull_request.synchronize', this.handler.bind(this));
    this.app.on('issue_comment.created', this.handler.bind(this));
    this.app.on('issue_comment.edited', this.handler.bind(this));
  }

2. If it's pull_request.* event, it will try to run the default dispatch logic, which adds a ciflow/default label and then signal with assign/unassign event to the main pytorch/pytorch repo.

3. If it's issue_comment.* event, it first checks if the comment has keyword @pytorchbot ciflow ..., if it does, apply the default dispatch logic and send signals.

Deployment note

• [x] make sure the pytorchbot has the write permission of pull_request on pytorch/pytorch
• [x] make sure the pytorchbot can listen to issue_comment events on pytorch/pytorch
• [x] deploy with the ENABLE_CIFLOWBOT=false and monitor errors
• [ ] deploy with the ENABLE_CIFLOWBOT=true and monitor errors (revert if something is wrong, finger crossed)