added api_app_id to slash command payload

[stevengill]

Summary

added api_app_id to slash command payload.

Issue: #573

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 #574 into main will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #574   +/-   ##
=======================================
  Coverage   83.24%   83.24%           
=======================================
  Files           7        7           
  Lines         597      597           
  Branches      193      193           
=======================================
  Hits          497      497           
  Misses         67       67           
  Partials       33       33           

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