Add ApplyPythonMutator

[kanterov]

Changes

Add ApplyPythonMutator, which will fork the Python subprocess and process pipe bundle configuration through it.

It's enabled through experimental section, for example:

experimental:
  enable_pydabs: true
  venv:
    path: .venv

For now, it's limited to two phases in the mutator pipeline:

• preinit: adds new jobs
• init: adds new jobs, or modifies existing ones

It's enforced that no jobs are modified in preinit and not jobs are deleted in preinit/init, because, otherwise, it will break existing assumptions.

This is stacked on top of https://github.com/databricks/cli/pull/1428

Tests

Unit tests

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 70.42254% with 42 lines in your changes missing coverage. Please review.

Project coverage is 54.96%. Comparing base (e22dd8a) to head (48d9328). Report is 146 commits behind head on main.

Files	Patch %	Lines
...ndle/config/mutator/python/apply_python_mutator.go	83.18%	10 Missing and 9 partials :warning:
libs/process/opts.go	0.00%	12 Missing :warning:
bundle/config/mutator/python/log_writer.go	28.57%	10 Missing :warning:
bundle/config/mutator/mutator.go	0.00%	1 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1430      +/-   ##
==========================================
+ Coverage   52.25%   54.96%   +2.71%     
==========================================
  Files         317      353      +36     
  Lines       18004    16238    -1766     
==========================================
- Hits         9408     8926     -482     
+ Misses       7903     6499    -1404     
- Partials      693      813     +120     

:umbrella: View full report in Codecov by Sentry.
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[kanterov]

@pietern can you please take a look, since the last time:

• merge.Override has changed, so now we implement OverrideVisitor here, I added tests for it as well
• left a bare minimum code to log stderr for the Python process, to be continued as a follow-up
• addressed remaining comments

[kanterov]

@pietern I've addressed all comments, and also renamed "pre-init" to "load" as we discussed offline

[kanterov]

@pietern thanks for the review, can you please add to the merge queue?