Use Dockerfile 1.4

[lucacome]

Improvements:

• Use --link to not invalidate the layer even if previous layers have changed (see docs)
• Use cache when building in container to speed up build and mount the directory removing the need to copy the source code.

[codecov-commenter]

Codecov Report

Merging #2567 (71a1359) into main (89a49b7) will decrease coverage by 0.01%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #2567      +/-   ##
==========================================
- Coverage   53.52%   53.50%   -0.02%     
==========================================
  Files          49       49              
  Lines       14314    14314              
==========================================
- Hits         7661     7659       -2     
  Misses       6412     6412              
- Partials      241      243       +2     

Impacted Files	Coverage Δ
internal/k8s/configuration.go	95.47% <0.00%> (-0.39%)	⬇️
...ternal/k8s/appprotect/app_protect_configuration.go	86.74% <0.00%> (+0.57%)	⬆️

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