Move static files to scratch image

[lucacome]

Proposed changes

Moves nginx static files to a scratch image.
With ADD --link we can cache the files instead of downloading them every time.
It also removes the need for curl/wget and switches from gpg to https://sequoia-pgp.org/ that has fewer dependencies.

[codecov]

Codecov Report

Merging #4551 (ac72731) into main (e277674) will not change coverage.
The diff coverage is n/a.

❗ Current head ac72731 differs from pull request most recent head d349946. Consider uploading reports for the commit d349946 to get more accurate results

@@           Coverage Diff           @@
##             main    #4551   +/-   ##
=======================================
  Coverage   51.97%   51.97%           
=======================================
  Files          59       59           
  Lines       16962    16962           
=======================================
  Hits         8816     8816           
  Misses       7849     7849           
  Partials      297      297           

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[shaun-nx]

👏