fix(sync): more descriptive error for custom build inferred sync misconfiguration

[nkubala]

fixes: #6772

this change improves the error message we surface when an inferred sync rule is configured with a custom builder that doesn't have the required dependencies.

[codecov]

Codecov Report

Merging #6778 (2cc83b4) into main (290280e) will decrease coverage by 1.36%.
The diff coverage is 77.08%.

@@            Coverage Diff             @@
##             main    #6778      +/-   ##
==========================================
- Coverage   70.48%   69.11%   -1.37%     
==========================================
  Files         515      547      +32     
  Lines       23150    25029    +1879     
==========================================
+ Hits        16317    17299     +982     
- Misses       5776     6567     +791     
- Partials     1057     1163     +106     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/deploy.go	52.00% <ø> (-1.85%)	⬇️
cmd/skaffold/app/cmd/flags.go	91.00% <ø> (+0.18%)	⬆️
cmd/skaffold/app/cmd/render.go	36.66% <0.00%> (-4.72%)	⬇️
cmd/skaffold/skaffold.go	0.00% <ø> (ø)
cmd/skaffold/app/cmd/lint.go	42.85% <60.00%> (ø)
cmd/skaffold/app/cmd/cmd.go	72.13% <100.00%> (+1.07%)	⬆️
cmd/skaffold/app/cmd/debug.go	100.00% <100.00%> (ø)
cmd/skaffold/app/cmd/runner.go	64.17% <100.00%> (ø)
cmd/skaffold/app/flags/image.go	76.27% <100.00%> (+3.72%)	⬆️
cmd/skaffold/app/skaffold.go	76.19% <100.00%> (-8.43%)	⬇️
... and 160 more

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[briandealwis]

Looks like there are some build failures here @nkubala

[briandealwis]

Can you take a look at these test errors @nkubala?

[MarlonGamez]

Have a question about the need for two separate errors here