feat(service): github, conditional requests

[JosephKav]

reduce likelihood of api rate-limiting
https://docs.github.com/en/rest/overview/resources-in-the-rest-api#conditional-requests

[codecov]

Codecov Report

Merging #176 (a2055f5) into master (b15e8ae) will increase coverage by 0.02%.
The diff coverage is 100.00%.

❗ Current head a2055f5 differs from pull request most recent head 68bf0ac. Consider uploading reports for the commit 68bf0ac to get more accurate results

@@            Coverage Diff             @@
##           master     #176      +/-   ##
==========================================
+ Coverage   97.65%   97.66%   +0.02%     
==========================================
  Files          63       63              
  Lines        5264     5296      +32     
==========================================
+ Hits         5140     5172      +32     
  Misses         89       89              
  Partials       35       35              

Impacted Files	Coverage Δ
service/latest_version/init.go	100.00% <100.00%> (ø)
service/latest_version/query.go	98.43% <100.00%> (+0.29%)	⬆️

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