Add thread_ts to RespondFn type

[misscoded]

Summary

Adds missing optional thread_ts to respond function. See documentation for reference.

Related to #2170.

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

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 93.44%. Comparing base (949226c) to head (db73642).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #2732   +/-   ##
=======================================
  Coverage   93.44%   93.44%           
=======================================
  Files          37       37           
  Lines        7674     7675    +1     
  Branches      669      669           
=======================================
+ Hits         7171     7172    +1     
  Misses        498      498           
  Partials        5        5           

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