feat: initial GitHub support

[jippi]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 0% with 424 lines in your changes are missing coverage. Please review.

Project coverage is 0.00%. Comparing base (d71528c) to head (e394546).

Files	Patch %	Lines
pkg/scm/helpers.go	0.00%	95 Missing ⚠️
pkg/scm/github/client_actioner.go	0.00%	74 Missing ⚠️
pkg/scm/github/client_label.go	0.00%	57 Missing ⚠️
pkg/scm/github/context.go	0.00%	44 Missing ⚠️
pkg/scm/github/context_pull_request.go	0.00%	25 Missing ⚠️
pkg/scm/github/client_pull_request.go	0.00%	21 Missing ⚠️
pkg/scm/github/client.go	0.00%	20 Missing ⚠️
pkg/state/context.go	0.00%	14 Missing ⚠️
cmd/shared.go	0.00%	11 Missing ⚠️
pkg/scm/github/client_helpers.go	0.00%	10 Missing ⚠️
... and 10 more

Additional details and impacted files

@@          Coverage Diff           @@
##            main     #18    +/-   ##
======================================
  Coverage   0.00%   0.00%            
======================================
  Files         30      39     +9     
  Lines       1329    1783   +454     
======================================
- Misses      1329    1783   +454     

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