Fixed uploading best model checkpoint in NeptuneLogger

[Raalsky]

What does this PR do?

Fixes #10602

Adds best model checkpoint uploading to NeptuneLogger.

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

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Make sure you had fun coding 🙃

[awaelchli]

Seems our codeowners github trigger did not work. They were not requested for review.
https://github.com/PyTorchLightning/pytorch-lightning/blob/edbf27430d02b59da717a870d98154f3dbea8ff1/.github/CODEOWNERS#L29

Pinging them manually for now:
@shnela @HubertJaworski @pkasprzyk @pitercl @Raalsky @aniezurawski @kamil-kaczmarek
Could one of you have a quick look? Thx

[kamil-kaczmarek]

@awaelchli
approved.

[rohitgr7]

mind update the chlog since 1.5.1 has been released?

[awaelchli]

The hanging tests were fixed on master. I tried to update the branch but don't have write access to push the changes. Could you please do it so we can merge the fix?

[Raalsky]

@awaelchli Is there anything should I take care of?

[awaelchli]

Nope, thanks for the reminder. Will check back once tests have run

[awaelchli]

Thanks @kamil-kaczmarek , this fix will be included next week in the bugfix release 1.5.5.

[kamil-kaczmarek]

Great thanks, kudos to @Raalsky for leading this bug fix 🎉