Fix default logging levels for train step specific hooks

[rohitgr7]

What does this PR do?

The following hooks had levels on_step=False and on_epoch=True by default:

on_train_batch_start
on_train_batch_end
on_before_backward
on_after_backward
on_before_optimizer_step
on_before_zero_grad

now they are logged with on_step=True and on_epoch=False by default. Also added a test to check for default levels for all hooks.

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

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.
Before you start reviewing make sure you have read Review guidelines. In short, see the following bullet-list:

• 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

Did you have fun?

Make sure you had fun coding 🙃

cc @Borda @carmocca @edward-io @ananthsub

[github-actions]

Build Error! No Linked Issue found. Please link an issue or mention it in the body using #<issue_id>

[codecov]

Codecov Report

Merging #10756 (af16094) into master (e507bc9) will decrease coverage by 0%.
The diff coverage is 94%.

❗ Current head af16094 differs from pull request most recent head 1801937. Consider uploading reports for the commit 1801937 to get more accurate results

@@           Coverage Diff           @@
##           master   #10756   +/-   ##
=======================================
- Coverage      92%      92%   -0%     
=======================================
  Files         177      177           
  Lines       16435    16397   -38     
=======================================
- Hits        15088    15052   -36     
+ Misses       1347     1345    -2     

[tchaton]

LGTM !