Add support for repo setting use_squash_pr_title_as_default

[garrettheel]

Adds support for the repository setting use_squash_pr_title_as_default.

Related API docs:
https://docs.github.com/en/rest/repos/repos#get-a-repository
https://docs.github.com/en/rest/repos/repos#create-an-organization-repository
https://docs.github.com/en/rest/repos/repos#update-a-repository

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[gmlewis]

Thank you, @garrettheel !
Just a few minor tweaks, please, before we merge.

[codecov]

Codecov Report

Merging #2390 (1dc51d6) into master (697804f) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master    #2390   +/-   ##
=======================================
  Coverage   98.06%   98.06%           
=======================================
  Files         119      119           
  Lines       10545    10546    +1     
=======================================
+ Hits        10341    10342    +1     
  Misses        140      140           
  Partials       64       64           

Impacted Files	Coverage Δ
github/repos.go	98.66% <100.00%> (+<0.01%)	⬆️

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[garrettheel]

@gmlewis thanks for reviewing, addressed your comments!

[gmlewis]

Thank you, @garrettheel !
LGTM.
Merging.