standardize on num_iter and max_num_iter keyword names

[grlee77]

Description

This PR addresses one of the cases discussed in #4154.

There is no change in behavior aside from the deprecation warnings when an old parameter name is provided. These warnings are explicitly tested via expected_warnings

Checklist

• Docstrings for all functions
• Gallery example in ./doc/examples (new features only)
• Benchmark in ./benchmarks, if your changes aren't covered by an
  existing benchmark
• Unit tests
• Clean style in the spirit of PEP8

For reviewers

• Check that the PR title is short, concise, and will make sense 1 year
  later.
• Check that new functions are imported in corresponding __init__.py.
• Check that new features, API changes, and deprecations are mentioned in
  doc/release/release_dev.rst.

[pep8speaks]

Hello @grlee77! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-06-26 21:58:57 UTC

[rfezzani]

Excellent! Thank you again @grlee77 😉