#999 Adds Slack Connect API event types

[srajiang]

Summary

Fixes #999 by adding event types for the Slack Connect APIs.

For reviewers: I wanted to take note of the fact that as of writing, the event type signatures listed on the api documentation site for the above are incorrect and need to be fixed (it's been noted internally).

So I based these types on 1) internal examples of event payloads 2) technical spec and 3) confirmation from BE-engineer maintaining these endpoints. If reviewers think that it'd be best to merge these changes only after public docs are corrected, we can also hold off on merging.

Reference types:

• shared_channel_invite_received
• shared_channel_invite_accepted
• shared_channel_invite_approved
• shared_channel_invite_declined

Requirements (place an x in each [ ])

• 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.

[codecov]

Codecov Report

Merging #1008 (84b2678) into main (4fff0f7) will not change coverage.
The diff coverage is n/a.

❗ Current head 84b2678 differs from pull request most recent head b5c01b4. Consider uploading reports for the commit b5c01b4 to get more accurate results

@@           Coverage Diff           @@
##             main    #1008   +/-   ##
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  Coverage   68.89%   68.89%           
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  Files          13       13           
  Lines        1212     1212           
  Branches      357      357           
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  Hits          835      835           
  Misses        304      304           
  Partials       73       73           

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[filmaj]

If reviewers think that it'd be best to merge these changes only after public docs are corrected, we can also hold off on merging.

This seems prudent to me - being able to reference something public in the PR that you based the work off of draws a nice line from the source to your changes. That said, I'm new on the team, so I am not familiar with how things are done 'round these parts yet, and I defer to what the rest of the team usually does 😄

[srajiang]

@stevengill @filmaj's line of thinking I am following and liking, but defer to you on this in terms of waiting to merge these vs. prodding internally to get these corrected before finalizing these changes!

[srajiang]

@stevengill - Types have been updated in api.slack.com, and I've updated this PR with the changes. Should be finally ready for review!

[stevengill]

LGTM!