text: Title: Add an easier way to access Events API retry info
  Body: The issue #731 reminds me that https://github.com/slackapi/java-slack-sdk/pull/677 can be added to bolt-python (and possibly to bolt-js).
  
  ### Category (place an `x` in each of the `[ ]`)
  
  * [x] **slack_bolt.App** and/or its core components
  * [x] **slack_bolt.async_app.AsyncApp** and/or its core components
  * [ ] Adapters in **slack_bolt.adapter**
  * [ ] Others
  
  ## Requirements
  
  Please read the [Contributing guidelines](https://github.com/slackapi/bolt-python/blob/main/.github/contributing.md) and [Code of Conduct](https://slackhq.github.io/code-of-conduct) before creating this issue or pull request. By submitting, you are agreeing to those rules.
  