Add flag that prints timestamps in skaffold logs.

[jtzwu]

Description
Adds a flag that add timestamps to the skaffold logs.

User facing changes (remove if N/A)
Before

DEBU[0000] found config for context "minikube"          
DEBU[0000] could not parse date ""                      
DEBU[0000] Defaulting build type to local build         
INFO[0000] Using kubectl context: minikube        

After

DEBU[2020-12-22T17:05:27-08:00] found config for context "minikube"           
DEBU[2020-12-22T17:05:27-08:00] could not parse date ""                       
DEBU[2020-12-22T17:05:27-08:00] Defaulting build type to local build  

[codecov]

Codecov Report

Merging #5181 (996aef5) into master (056bc1d) will decrease coverage by 0.57%.
The diff coverage is 80.00%.

@@            Coverage Diff             @@
##           master    #5181      +/-   ##
==========================================
- Coverage   72.39%   71.82%   -0.58%     
==========================================
  Files         385      387       +2     
  Lines       13735    13928     +193     
==========================================
+ Hits         9944    10004      +60     
- Misses       3063     3190     +127     
- Partials      728      734       +6     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/cmd.go	67.40% <80.00%> (+0.99%)	⬆️
pkg/skaffold/diagnose/diagnose.go	15.15% <0.00%> (-39.40%)	⬇️
pkg/skaffold/build/dependencies.go	0.00% <0.00%> (-33.34%)	⬇️
pkg/skaffold/yaml/yaml.go	62.96% <0.00%> (-13.97%)	⬇️
pkg/skaffold/build/cache/lookup.go	80.00% <0.00%> (-7.88%)	⬇️
cmd/skaffold/app/cmd/test.go	46.66% <0.00%> (-7.18%)	⬇️
cmd/skaffold/app/cmd/deploy.go	56.52% <0.00%> (-5.39%)	⬇️
pkg/skaffold/test/test.go	86.79% <0.00%> (-5.37%)	⬇️
pkg/skaffold/runner/runcontext/context.go	79.27% <0.00%> (-5.34%)	⬇️
pkg/skaffold/errors/errors.go	86.95% <0.00%> (-4.35%)	⬇️
... and 32 more

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[MarlonGamez]

hey @jtzwu, thanks for opening this PR. Looks like there's a formatting issue here but that's a quick fix. You'll also need to run ./hack/generate-man.sh and commit the results to update our docs to reflect the added flag. Thanks!

[MarlonGamez]

lgtm 👍🏼