Mark GCP Buildpacks builder as trusted in the examples

[briandealwis]

Fixed #5971

Description
Mark our examples using the GCP Buildpacks builder (gcr.io/buildpacks/builder:v1) as a trusted builder. This setting causes the pack library to use the lifecycle that is in the image instead of trying to download and run the lifecycle-as-an-image.

(I'm unsure about retaining the digest in the buildpacks builder in the absence of tooling to automatically monitor and update digests, but left it in.)

This setting puts the user in charge and is simpler than having Skaffold maintain a list of trusted builders, or to see if it was possible to reuse the CNB project's method for trusted images.

[codecov]

Codecov Report

Merging #6284 (b97f8bf) into main (cf4aab8) will decrease coverage by 0.00%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #6284      +/-   ##
==========================================
- Coverage   70.49%   70.48%   -0.01%     
==========================================
  Files         498      498              
  Lines       22560    22581      +21     
==========================================
+ Hits        15903    15916      +13     
- Misses       5627     5635       +8     
  Partials     1030     1030              

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/cmd.go	71.50% <0.00%> (-2.16%)	⬇️
pkg/skaffold/deploy/kubectl/kubectl.go	67.45% <0.00%> (-0.57%)	⬇️
pkg/skaffold/runner/v1/apply.go	0.00% <0.00%> (ø)
pkg/skaffold/runner/v1/deploy.go	74.28% <0.00%> (ø)
pkg/skaffold/kubernetes/manifest/images.go	100.00% <0.00%> (ø)

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[MarlonGamez]

I think we'll need to rebase this to pull in #6311 for this to successfully build in kokoro @briandealwis