Add callback command

[dfarr]

Supersedes #446, thank you @Madraceee

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 97 lines in your changes missing coverage. Please review.

Project coverage is 56.39%. Comparing base (3009bbb) to head (74ba4a3).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
cmd/callbacks/create.go	0.00%	62 Missing ⚠️
cmd/callbacks/callbacks.go	0.00%	28 Missing ⚠️
cmd/tasks/claim.go	0.00%	3 Missing ⚠️
cmd/tasks/heartbeat.go	0.00%	3 Missing ⚠️
cmd/tasks/complete.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #499      +/-   ##
==========================================
- Coverage   56.71%   56.39%   -0.33%     
==========================================
  Files         120      122       +2     
  Lines       13171    13261      +90     
==========================================
+ Hits         7470     7478       +8     
- Misses       5249     5331      +82     
  Partials      452      452              

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