Enable file-watching for debug

[briandealwis]

Fixes #2351
Fixes #3272
Fixes #4129

Description

Pulls in the dev-like arguments to control image rebuilding and redeploying such as:

• --watch-image to restrict the images to be monitored
• --trigger — for this I kept the same "notify" default, but I wonder if manual would make more sense
• --auto-build, --auto-deploy, and --auto-sync but defaulting to false.

This at least allows users to enable rebuilding and redeploying on change, which is useful for Go in particular.

User facing changes

skaffold debug now supports listing images to watch and a watch-trigger, though they are essentially non-functional and not worth mentioning since --auto-build, --auto-deploy, and --auto-sync default to false, and are hidden.

[codecov]

Codecov Report

Merging #4089 into master will decrease coverage by 0.03%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4089      +/-   ##
==========================================
- Coverage   71.77%   71.74%   -0.04%     
==========================================
  Files         324      324              
  Lines       12499    12502       +3     
==========================================
- Hits         8971     8969       -2     
- Misses       2958     2965       +7     
+ Partials      570      568       -2     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/flags.go	86.36% <ø> (ø)
cmd/skaffold/app/cmd/debug.go	100.00% <100.00%> (ø)
cmd/skaffold/app/cmd/dev.go	82.85% <100.00%> (-3.81%)	⬇️
pkg/skaffold/deploy/resource/deployment.go	74.48% <0.00%> (-0.77%)	⬇️
pkg/skaffold/debug/transform_nodejs.go	80.86% <0.00%> (-0.33%)	⬇️
pkg/diag/validator/pod.go	1.28% <0.00%> (-0.07%)	⬇️
pkg/skaffold/debug/transform_jvm.go	94.62% <0.00%> (-0.06%)	⬇️
pkg/skaffold/event/event.go	90.59% <0.00%> (+0.07%)	⬆️
pkg/skaffold/debug/cnb.go	93.10% <0.00%> (+0.51%)	⬆️
pkg/skaffold/debug/transform_go.go	85.85% <0.00%> (+2.02%)	⬆️
... and 1 more

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[briandealwis]

PTAL @dgageot

[briandealwis]

Yeah, it works because it uses a different temporary variable. When I start skaffold debug in examples/getting-started, and then make a change to main.go, there are no rebuilds.

But you're right — I should make a test here.

[briandealwis]

PTAL @dgageot — added some tests to verify that the arguments are set and are independent of each other. I de-aliased dev too so that NewCmdDebug and NewCmdDev can be called independently of each other.

[briandealwis]

It turns out that our runner creation depends on the implicit initialization of the trigger type from Dev():

TestDeploy: helper.go:194: skaffold deploy: exit status 1, 
    TestDeploy: panic.go:617: creating runner: creating watch trigger: unsupported trigger: 

[briandealwis]

Using the common flags is much nicer.

[briandealwis]

PTAL @dgageot

changes addressed