Add an easier way to access Events API retry info #732

The issue #731 reminds me that slackapi/java-slack-sdk#677 can be added to bolt-python (and possibly to bolt-js).

Category (place an x in each of the [ ])

• slack_bolt.App and/or its core components
• slack_bolt.async_app.AsyncApp and/or its core components
• Adapters in slack_bolt.adapter
• Others

Requirements

Please read the Contributing guidelines and Code of Conduct before creating this issue or pull request. By submitting, you are agreeing to those rules.