skaffold debug should use debugpy for Python

[briandealwis]

Fixes: #4437

Description
This PR switches skaffold debug to use debugpy for Python from the now-deprecated ptvsd. It recognizes if ptvsd or debugpy is already in use. debugpy has been part of the debug helper images for a while now.

User facing changes (remove if N/A)
skaffold debug now uses debugpy for Python.

[gsquared94]

nit for consistency:

Suggested change

	if index := util.StrSliceIndex(args, "-m"+module); index >= 0 {
	if index := util.StrSliceIndex(args, fmt.Sprintf("-m%s", module)); index >= 0 {

[codecov]

Codecov Report

Merging #5576 (ca6b3ad) into master (5ed2556) will decrease coverage by 0.22%.
The diff coverage is 65.67%.

@@            Coverage Diff             @@
##           master    #5576      +/-   ##
==========================================
- Coverage   71.25%   71.03%   -0.23%     
==========================================
  Files         400      402       +2     
  Lines       14975    15096     +121     
==========================================
+ Hits        10671    10724      +53     
- Misses       3514     3578      +64     
- Partials      790      794       +4     

Impacted Files	Coverage Δ
pkg/skaffold/debug/transform_python.go	73.68% <65.67%> (-5.77%)	⬇️
cmd/skaffold/app/cmd/commands.go	81.25% <0.00%> (-9.00%)	⬇️
pkg/skaffold/deploy/kubectl/kubectl.go	65.18% <0.00%> (-1.48%)	⬇️
pkg/skaffold/runner/new.go	63.13% <0.00%> (ø)
pkg/skaffold/runner/runner.go	0.00% <0.00%> (ø)
pkg/skaffold/config/options.go	100.00% <0.00%> (ø)
pkg/skaffold/runner/changeset.go	77.77% <0.00%> (ø)
pkg/skaffold/deploy/kubectl/cli.go	87.50% <0.00%> (ø)
pkg/skaffold/runner/apply.go	0.00% <0.00%> (ø)
cmd/skaffold/app/cmd/apply.go	25.00% <0.00%> (ø)
... and 6 more

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 5ed2556...ca6b3ad. Read the comment docs.

[gsquared94]

lgtm!