Add log_weight_decay argument to LearningRateMonitor callback

[ioangatop]

What does this PR do?

Fixes #18117

Before submitting

• Was this discussed/agreed 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 minor internal changes/refactors)

PR review

Anyone in the community is welcome to review the PR.
Before you start reviewing, make sure you have read the review guidelines. In short, see the following bullet-list:

Reviewer checklist

• Is this pull request ready for review? (if not, please submit in draft mode)
• Check that all items from Before submitting are resolved
• Make sure the title is self-explanatory and the description concisely explains the PR
• Add labels and milestones (and optionally projects) to the PR so it can be classified

[codecov]

Codecov Report

Merging #18439 (2eff8d9) into master (c807bbb) will decrease coverage by 35%.
Report is 1 commits behind head on master.
The diff coverage is 100%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #18439      +/-   ##
==========================================
- Coverage      85%      50%     -35%     
==========================================
  Files         427      419       -8     
  Lines       33277    33143     -134     
==========================================
- Hits        28285    16613   -11672     
- Misses       4992    16530   +11538     

[carmocca]

LGTM