Add Python debugging support

[briandealwis]

This patch adds support to skaffold debug for Python 2.7 and 3.x debugging. Python requires additional debugging runtime support files, which are fetched and installed using an initContainer base.

These debugging runtime support files are installed via initContainers from images defined in https://github.com/GoogleContainerTools/container-debug-support/. These images are currently manually pushed to gcr.io/gcp-dev-tools/duct-tape/XXX where XXX is a runtime-specific identifier like python (supports both Python 2.7 and 3.7).

The Python image installs the ptvsd module, a wrapper that uses the IDE/editor-agnostic debug adapter protocol (DAP). This protocol has become a de facto standard for interacting with remote runtimes.

Manual Testing

For manual testing, you'll need to use VS Code or Eclipse with LSP4e, or some other editor that supports the DAP. I had to launch my debug session with the following launch parameters, to map the local file system to the remote file system in the container:

{"pathMappings": [ { "localRoot": "_/your/local/path_", "remoteRoot": "/app" }]}

The debugger is on port 5678.

Fixes #2173

[codecov-io]

Codecov Report

Merging #2205 into master will increase coverage by 0.45%.
The diff coverage is 87.12%.

@@            Coverage Diff             @@
##           master    #2205      +/-   ##
==========================================
+ Coverage    58.6%   59.06%   +0.45%     
==========================================
  Files         188      189       +1     
  Lines        7805     7924     +119     
==========================================
+ Hits         4574     4680     +106     
- Misses       2859     2866       +7     
- Partials      372      378       +6

Impacted Files	Coverage Δ
pkg/skaffold/util/util.go	76.59% <100%> (+1.04%)	⬆️
pkg/skaffold/debug/transform_jvm.go	94.89% <100%> (+0.1%)	⬆️
pkg/skaffold/debug/debug.go	44.82% <50%> (ø)	⬆️
pkg/skaffold/debug/transform_nodejs.go	79.24% <66.66%> (+0.39%)	⬆️
pkg/skaffold/debug/transform_python.go	85.55% <85.55%> (ø)
pkg/skaffold/debug/transform.go	85.03% <96%> (+2.63%)	⬆️

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[ILMTitan]

"debugging-support-files" is used on multiple lines. Extract to constant?

[loosebazooka]

Just some stuff to clarify things for me?

[briandealwis]

PTAL @loosebazooka @ILMTitan

[briandealwis]

@quoctruong PTAL

[loosebazooka]

Just some language stuff I'm not sure about, feel free to ignore or whatever.

[loosebazooka]

Also might be worth doing a ux study with the team to see if we can all follow the instructions 🛩️

[briandealwis]

PTAL @dgageot @balopat — need your approvals due to doc changes

[balopat]

LGTM.

Re Approvals: you had changes in a main util file hence our review was required. Also more "debug" related files were changed for integration testing that weren't owned by you, so I added those to the CODEOWNERS in #2292