Add github api token option to generate-license & generate-gitignore

[zeripath]

Continued from #12683.

Without providing the username and token both of these commands could be rate limited.

This PR provides a way of setting the username and token to be set over BASIC authentication to prevent rate limiting.

[codecov-commenter]

Codecov Report

Merging #12700 into master will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master   #12700      +/-   ##
==========================================
- Coverage   43.31%   43.30%   -0.01%     
==========================================
  Files         646      646              
  Lines       71567    71567              
==========================================
- Hits        30997    30995       -2     
- Misses      35552    35556       +4     
+ Partials     5018     5016       -2     

Impacted Files	Coverage Δ
modules/git/utils.go	73.77% <0.00%> (-3.28%)	⬇️
services/pull/check.go	47.69% <0.00%> (-2.31%)	⬇️
modules/log/event.go	56.60% <0.00%> (-1.89%)	⬇️
models/error.go	34.81% <0.00%> (-0.52%)	⬇️
modules/git/repo.go	49.23% <0.00%> (-0.51%)	⬇️
models/issue_comment.go	53.75% <0.00%> (-0.16%)	⬇️
services/pull/pull.go	42.72% <0.00%> (+1.15%)	⬆️
modules/git/blame.go	77.19% <0.00%> (+1.75%)	⬆️
services/pull/temp_repo.go	29.78% <0.00%> (+3.19%)	⬆️
services/pull/update.go	57.69% <0.00%> (+5.76%)	⬆️

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