Fix Bug that prevents showing survey prompt

[IsaacPD]

Fix bug I introduced where the survey prompt will only show if os.Stdout does not support colors i.e. when color.SetupColors(out, forceColors) does not wrap out.

Description

Fixed by actually checking if the passed io.Writer is a wrapped colorableWriter. Added a test case to ensure that color.IsStdout(color.NewWriter(os.Stdout)) returns true

Before (master):
With an empty global config and running skaffold build in examples/getting-started, the survey prompt does not show up. This is because survey.isStdout(out) returns false when out = colorableWriter{os.Stdout}.

After:
Survey prompt shows up given the same conditions above.

[codecov]

Codecov Report

Merging #5027 (f13b0fb) into master (e685dd2) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #5027      +/-   ##
==========================================
- Coverage   72.19%   72.18%   -0.02%     
==========================================
  Files         365      365              
  Lines       12840    12859      +19     
==========================================
+ Hits         9270     9282      +12     
- Misses       2880     2886       +6     
- Partials      690      691       +1     

Impacted Files	Coverage Δ
pkg/skaffold/survey/survey.go	41.66% <ø> (-4.49%)	⬇️
pkg/skaffold/color/formatter.go	100.00% <100.00%> (ø)
pkg/skaffold/runner/load_images.go	94.73% <0.00%> (-5.27%)	⬇️
pkg/skaffold/build/cache/hash.go	71.28% <0.00%> (-2.12%)	⬇️
pkg/skaffold/docker/dependencies.go	73.33% <0.00%> (-1.67%)	⬇️
pkg/skaffold/deploy/helm/helm.go	73.73% <0.00%> (-0.07%)	⬇️
pkg/skaffold/util/store.go	100.00% <0.00%> (ø)

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[MarlonGamez]

This looks good to me. Nice catch on that bug 👍🏼