feat: new dockerfiles and cloudbuild config for slim image

[renzodavid9]

Fixes: #6637

Description
This PR adds new Dockerfiles and a cloudbuild-slim.yaml configuration to trigger the creation of a skaffold slim image with every push to main branch.

The slim image is a copy of the lts version which has less dependencies that the edge version.

[codecov]

Codecov Report

Merging #7996 (1b17676) into main (290280e) will decrease coverage by 3.75%.
The diff coverage is 54.09%.

@@            Coverage Diff             @@
##             main    #7996      +/-   ##
==========================================
- Coverage   70.48%   66.73%   -3.76%     
==========================================
  Files         515      596      +81     
  Lines       23150    28894    +5744     
==========================================
+ Hits        16317    19281    +2964     
- Misses       5776     8193    +2417     
- Partials     1057     1420     +363     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/credits/export.go	0.00% <0.00%> (ø)
cmd/skaffold/app/cmd/deploy.go	40.90% <0.00%> (-12.94%)	⬇️
cmd/skaffold/app/cmd/test.go	44.44% <0.00%> (ø)
cmd/skaffold/app/exitcode.go	100.00% <ø> (+6.66%)	⬆️
cmd/skaffold/skaffold.go	0.00% <0.00%> (ø)
cmd/skaffold/app/cmd/inspect_tests.go	62.50% <14.28%> (-1.14%)	⬇️
cmd/skaffold/app/cmd/render.go	35.48% <18.18%> (-5.90%)	⬇️
cmd/skaffold/app/cmd/lsp.go	28.12% <28.12%> (ø)
cmd/skaffold/app/cmd/run.go	64.28% <33.33%> (-9.63%)	⬇️
cmd/skaffold/app/cmd/fix.go	56.41% <37.50%> (-20.07%)	⬇️
... and 390 more

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[aaron-prindle]

LGTM!