skaffold deploy -t flag

[anshlykov]

Fixes: #4455

Description
This PR adds the --tag flag to the deploy command. If the '--tag' flag is present, then the tags for all artifacts are overridden.

Perhaps the deploy command should only use the new tag for artifacts for which the image tag is not explicitly specified. Let me know if I need to change anything.

[codecov]

Codecov Report

Merging #4778 into master will increase coverage by 0.00%.
The diff coverage is 77.77%.

@@           Coverage Diff           @@
##           master    #4778   +/-   ##
=======================================
  Coverage   73.84%   73.85%           
=======================================
  Files         347      347           
  Lines       13753    13825   +72     
=======================================
+ Hits        10156    10210   +54     
- Misses       2965     2976   +11     
- Partials      632      639    +7     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/flags.go	86.36% <ø> (ø)
cmd/skaffold/app/cmd/deploy.go	69.64% <76.47%> (+2.97%)	⬆️
pkg/skaffold/build/tag/util.go	90.90% <80.00%> (-9.10%)	⬇️
pkg/skaffold/build/cache/lookup.go	88.73% <0.00%> (-11.27%)	⬇️
pkg/skaffold/build/cache/details.go	13.79% <0.00%> (-1.03%)	⬇️
pkg/skaffold/docker/parse.go	89.05% <0.00%> (-0.90%)	⬇️
pkg/skaffold/deploy/helm.go	78.89% <0.00%> (+0.11%)	⬆️
pkg/skaffold/runner/new.go	68.18% <0.00%> (+0.63%)	⬆️
pkg/skaffold/build/cache/cache.go	57.77% <0.00%> (+0.95%)	⬆️
pkg/skaffold/build/cache/retrieve.go	70.65% <0.00%> (+1.33%)	⬆️
... and 1 more

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[MarlonGamez]

Thanks for making the change :) we're having some issues with CI right now so I'm gonna approve this and I'll merge it once we get stuff working again