Deprecate agg_key_funcs, agg_default_func, and update_agg_funcs from LightningLoggerBase

[akashkw]

What does this PR do?

Deprecates agg_key_funcs, agg_default_func and update_agg_funcs from LightningLoggerBase.

Part of #11235
Part of #9145

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 🙃

[edward-io]

Code looks good. For the deprecation message, can we add more information on what alternatives users could use?

[daniellepintz]

Can you also deprecate these in this PR, or were you planning to do this in another PR?
https://github.com/PyTorchLightning/pytorch-lightning/blob/79c4e5de60685dbc895641b0139ffc6180d069aa/pytorch_lightning/loggers/base.py#L102-L146

For these methods, you can put the dep. message in the docstring, but no need to send out a dep warning

[akashkw]

Code looks good. For the deprecation message, can we add more information on what alternatives users could use?

@edward-io Since the aggregation logic is in the training loop now, I'm not sure how (or if) a user can provide custom aggregation functions. Do you know what alternatives there might be?

[akashkw]

Can you also deprecate these in this PR, or were you planning to do this in another PR?

I think it makes sense to include in this PR #11832

[edward-io]

Code looks good. For the deprecation message, can we add more information on what alternatives users could use?

@edward-io Since the aggregation logic is in the training loop now, I'm not sure how (or if) a user can provide custom aggregation functions. Do you know what alternatives there might be?

Mentioning this in the deprecation message would be sufficient IMO, but this is just a nit. :)

[daniellepintz]

Since the aggregation logic is currently a no-op, I don't think it's necessary to mention any alternatives to users, since we are not really removing any functionality. I suppose we could mention the fact that the agg logic is a no-op, but not sure if we want to say that to users.