feat: implement dpkg-sig Package signing

[caarlos0]

continuing #508

[codecov]

Codecov Report

Merging #515 (b217db6) into main (1eb3837) will increase coverage by 0.19%.
The diff coverage is 60.86%.

@@            Coverage Diff             @@
##             main     #515      +/-   ##
==========================================
+ Coverage   65.97%   66.16%   +0.19%     
==========================================
  Files          16       16              
  Lines        2019     2013       -6     
==========================================
  Hits         1332     1332              
+ Misses        537      533       -4     
+ Partials      150      148       -2     

Impacted Files	Coverage Δ
internal/sign/pgp.go	65.31% <0.00%> (+1.38%)	⬆️
deb/deb.go	71.42% <63.63%> (+0.21%)	⬆️

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[erikgeiser]

LGTM. This PR doesn't contain unit tests for the new signing method though. I don't think that's a problem because the PR does add acceptance tests but I like the unit tests because they are way faster and more convenient. But overall it's not a big deal and you could just merge it.

[caarlos0]

@erikgeiser the unit tests were added in #508

main issue in this pr imo is that it does not actually verify the signing, as I couldn't find any way of doing it with a custom signature...

maybe @SasSwart knows a way?