fix(typescript): accept empty list of suggested prompts for the assistant class

[zimeg]

Summary

This PR accepts empty arrays for the assistant class set suggested prompts to improve typescript inference with empty arrays. Fixes #2506.

Preview

The changes of slack-samples/bolt-js-assistant-template#48 showcase this fix:

https://github.com/slack-samples/bolt-js-assistant-template/blob/b9fb90d60797fa71d346391c25ca61a331b6350f/app.js#L61-L70

Reviewers

Changes to a sample app can confirm this behavior! 👾

$ npm pack       # Package Bolt JS
$ slack create asdf -t slack-samples/bolt-js-assistant-template -b zimeg-fix-suggested-prompts-types
$ cd asdf
$ npm run check  # Expect errors
$ npm install /path/to/bolt-js/slack-bolt-4.4.0.tgz  # Use the packaged version
$ npm run check  # Expect no errors!

Notes

This change matches an upstream changes to @slack/web-api in slackapi/node-slack-sdk#2297 🌚 ✨

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.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.37%. Comparing base (150f0bd) to head (d8e6264).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2650   +/-   ##
=======================================
  Coverage   93.37%   93.37%           
=======================================
  Files          37       37           
  Lines        7581     7581           
  Branches      667      667           
=======================================
  Hits         7079     7079           
  Misses        497      497           
  Partials        5        5           

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[WilliamBergamin]

Sweet thanks for working on this 🚀

[zimeg]

@WilliamBergamin Likewise thanks for suggesting these changes and for the kind review!