Add support for npm run-script-based launches for skaffold debug

[briandealwis]

Fixes #2044

Adds support for launches by passing the node --inspect=xxxx option via npm's --node-options command line argument. This must appear after the run-script but before a -- (should it be present). npm uses this --node-options argument to configure the NODE_OPTIONS environment which is picked up by NodeJS 8 and higher.

Note: npm run-scripts that use nodemon (a node-based script) instead of node will not work as nodemon's node will interpret the NODE_OPTIONS and configure itself for debugging.

• add limitations to docs
• add debug integration tests for jib, nodejs, and npm artifacts

[codecov-io]

Codecov Report

Merging #2141 into master will increase coverage by 0.06%.
The diff coverage is 80.55%.

@@            Coverage Diff             @@
##           master    #2141      +/-   ##
==========================================
+ Coverage   56.31%   56.37%   +0.06%     
==========================================
  Files         180      180              
  Lines        7815     7858      +43     
==========================================
+ Hits         4401     4430      +29     
- Misses       2994     3007      +13     
- Partials      420      421       +1

Impacted Files	Coverage Δ
pkg/skaffold/debug/transform_jvm.go	94.79% <100%> (-0.06%)	⬇️
pkg/skaffold/util/util.go	67.62% <100%> (+1.93%)	⬆️
pkg/skaffold/debug/transform_nodejs.go	78.84% <74.07%> (-3.92%)	⬇️
pkg/skaffold/debug/transform.go	82.4% <0%> (-3.8%)	⬇️
cmd/skaffold/app/cmd/cmd.go	73.33% <0%> (-0.93%)	⬇️
cmd/skaffold/app/cmd/config/list.go	23.52% <0%> (ø)	⬆️
cmd/skaffold/man/man.go	77.27% <0%> (ø)	⬆️

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[chanseokoh]

The Maven test project looks good.

[balopat]

LGTM, thank you