[DOC] Code use of "estimator" term in base object interfaces

[tpvasconcelos]

Reference Issues/PRs

Depends on https://github.com/sktime/skbase/pull/281

What does this implement/fix? Explain your changes.

See https://github.com/sktime/skbase/pull/281#issuecomment-1956646894 and relevant replies.

What should a reviewer concentrate their feedback on?

PR checklist

For all contributions

• [x] I've reviewed the project documentation on contributing
• [x] I've added myself to the list of contributors.
• [x] The PR title starts with either [ENH], [CI/CD], [MNT], [DOC], or [BUG] indicating whether the PR topic is related to enhancement, CI/CD, maintenance, documentation, or a bug.

For code contributions

• [x] Unit tests have been added covering code functionality
• [x] Appropriate docstrings have been added (see documentation standards)
• [x] New public functionality has been added to the API Reference

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 62.50000% with 9 lines in your changes missing coverage. Please review.

Project coverage is 84.29%. Comparing base (306958d) to head (da1e4ab). Report is 67 commits behind head on main.

Files with missing lines	Patch %	Lines
skbase/base/_base.py	62.50%	9 Missing :warning:

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #293      +/-   ##
==========================================
- Coverage   85.07%   84.29%   -0.78%     
==========================================
  Files          45       45              
  Lines        3015     3184     +169     
==========================================
+ Hits         2565     2684     +119     
- Misses        450      500      +50     

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[tpvasconcelos]

@fkiraly I think this is ready to merge/review 👍

[fkiraly]

@tpvasconcelos, are you still working on this?