Add the ability to slack API to query saved messages

[hendrysadrak]

Description

I would like to have the opportunity for reflecting saved messages in another todo tool. When I save a message, I want a todo item to be created, and when unsaving, it to be deleted/completed.

This would mean adding one or both of the following solutions:

• Ability for querying the saved messages with the Slack API
• Have events for 'message saved' and 'message unsaved' in Events API

What type of issue is this?

• bug
• enhancement (feature request)
• question
• documentation related
• testing related
• discussion

Requirements

• I've read and understood the Contributing guidelines and have done my best effort to follow them.
• I've read and agree to the Code of Conduct.
• I've searched for any related issues and avoided creating a duplicate issue.