Add docstrings to Test Tube logger

[bamblebam]

What does this PR do?

Links #9028
Adds doc strings in the test tube logger class.

Does your PR introduce any breaking changes? If yes, please list them.

None

Before submitting

• Was this discussed/approved via a GitHub issue? (not for typos and docs)
• Did you read the contributor guideline, Pull Request section?
• Did you make sure your PR does only one thing, instead of bundling different changes together?
• Did you make sure to update the documentation with your changes? (if necessary)
• Did you write any new necessary tests? (not for typos and docs)
• Did you verify new and existing tests pass locally with your changes?
• Did you list all the breaking changes introduced by this pull request?
• Did you update the CHANGELOG? (not for typos, docs, test updates, or internal minor changes/refactorings)

PR review

Anyone in the community is welcome to review the PR.
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Did you have fun?

Make sure you had fun coding 🙃

[codecov]

Codecov Report

Merging #9110 (b7a3748) into master (1a2468f) will decrease coverage by 4%.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master   #9110    +/-   ##
=======================================
- Coverage      92%     88%    -4%     
=======================================
  Files         178     176     -2     
  Lines       14694   14666    -28     
=======================================
- Hits        13526   12889   -637     
- Misses       1168    1777   +609     

[tchaton]

LGTM !