Add buffered logger to the Python bootloader

[jrmccluskey]

Adds the buffered logger type to the Python bootloader script, capturing subprocess output and assigning an appropriate severity to them over the FnAPI (debug if the subprocess returns exit code 0, error if the subprocess returns exit code 1.) Also removes the quiet directive from pip invocations so full output is captured.

Example of new pip output, with package information logged appropriately:

---

Thank you for your contribution! Follow this checklist to help us incorporate your contribution quickly and easily:

• Mention the appropriate issue in your description (for example: addresses #123), if applicable. This will automatically add a link to the pull request in the issue. If you would like the issue to automatically close on merging the pull request, comment fixes #<ISSUE NUMBER> instead.
• Update CHANGES.md with noteworthy changes.
• If this contribution is large, please file an Apache Individual Contributor License Agreement.

See the Contributor Guide for more tips on how to make review process smoother.

To check the build health, please visit https://github.com/apache/beam/blob/master/.test-infra/BUILD_STATUS.md

GitHub Actions Tests Status (on master branch)

See CI.md for more information about GitHub Actions CI or the workflows README to see a list of phrases to trigger workflows.

[jrmccluskey]

CC: @tvalentyn

[codecov]

Codecov Report

Merging #28317 (8cd24ca) into master (7c1c250) will decrease coverage by 0.02%.
Report is 13 commits behind head on master.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master   #28317      +/-   ##
==========================================
- Coverage   72.34%   72.33%   -0.02%     
==========================================
  Files         680      680              
  Lines      100280   100323      +43     
==========================================
+ Hits        72552    72566      +14     
- Misses      26152    26184      +32     
+ Partials     1576     1573       -3     

Flag	Coverage Δ
go	53.60% <100.00%> (-0.01%)	⬇️
python	82.89% <ø> (-0.04%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files Changed	Coverage Δ
sdks/go/container/tools/buffered_logging.go	68.96% <100.00%> (ø)

... and 11 files with indirect coverage changes

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[github-actions]

Assigning reviewers. If you would like to opt out of this review, comment assign to next reviewer:

R: @tvalentyn for label python.
R: @lostluck for label go.

Available commands:

• stop reviewer notifications - opt out of the automated review tooling
• remind me after tests pass - tag the comment author after tests pass
• waiting on author - shift the attention set back to the author (any comment or push by the author will return the attention set to the reviewers)

The PR bot will only process comments in the main thread (not review comments).

[jrmccluskey]

Run PythonLint PreCommit

[jrmccluskey]

@damccorm