Add support for setting actions permissions on a repository

[h2floh]

👋 Hello there!

Couldn't find a PR for it yet so added functionality requested in #2297
Sorry if I pushed myself before @cfarrend in doing it but I will need the changes.

Went through the contributing guide and also added an example to test the change end2end.

Thanks everyone!

Fixes: #2297.

[google-cla]

Thanks for your pull request! It looks like this may be your first contribution to a Google open source project. Before we can look at your pull request, you'll need to sign a Contributor License Agreement (CLA).

For more information, open the CLA check for this pull request.

[codecov]

Codecov Report

Merging #2315 (ddff22b) into master (f859098) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #2315      +/-   ##
==========================================
+ Coverage   97.84%   97.85%   +0.01%     
==========================================
  Files         115      117       +2     
  Lines       10416    10466      +50     
==========================================
+ Hits        10192    10242      +50     
  Misses        156      156              
  Partials       68       68              

Impacted Files	Coverage Δ
github/orgs_actions_allowed.go	100.00% <ø> (ø)
github/repos_actions_allowed.go	100.00% <100.00%> (ø)
github/repos_actions_permissions.go	100.00% <100.00%> (ø)

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[h2floh]

Hey @gmlewis , I signed the ICLA after my company asked me to do that. Can you please rerun the cla check. Thanks!

[gmlewis]

Thank you, @h2floh !
Just a few tweaks, please, then we should be ready for a second review before merging.

[gmlewis]

@Parker77 - do you have time for a code review?

[gmlewis]

Thank you, @h2floh !
LGTM.

Awaiting second LGTM before merging.

[Parker77]

LGTM.

[gmlewis]

Thank you, @Parker77 !
Merging.