Use ProtonMail fork of crypto package for openpgp

[alexjplant]

Changes

Use the ProtonMail fork of the golang crypto package for openpgp per the GoLang recommendation and the go-crypto docs:

This module is backwards compatible with x/crypto/openpgp, so you can simply replace all imports of golang.org/x/crypto/openpgp with github.com/ProtonMail/go-crypto/openpgp.

Why Are Changes Being Made

To stop the linter from breaking the build

[codecov-commenter]

Codecov Report

Merging #64 (a8b6846) into master (e3ea999) will increase coverage by 0.45%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master      #64      +/-   ##
==========================================
+ Coverage   40.87%   41.33%   +0.45%     
==========================================
  Files          79       79              
  Lines        3053     3053              
==========================================
+ Hits         1248     1262      +14     
+ Misses       1545     1534      -11     
+ Partials      260      257       -3     

Impacted Files	Coverage Δ
internal/audittrail/storage_blob.go	55.55% <ø> (ø)
internal/gpgx/keys.go	48.00% <0.00%> (ø)
internal/transform/gpg.go	66.66% <ø> (ø)
internal/upload/sftp.go	65.04% <0.00%> (+2.42%)	⬆️
internal/pipeline/file_receiver.go	32.25% <0.00%> (+9.67%)	⬆️

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