upload checkpoint files to neptune from stream

[AleksanderWWW]

What does this PR do?

Fixes (issue on neptune-client repo):
neptune-ai/neptune-client#884

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[Blaizzy]

LGTM

[awaelchli]

Thanks for working on this @AleksanderWWW
I left a comment for fixing the tests, let me know if you need help with it.
We could also add an entry in the changelog in src/lightning/pytorch/CHANGELOG.md in the "#Fixed" section. Thanks!

[AleksanderWWW]

@awaelchli Thank you for the feedback! Let me know if the relevant commit is enough to move forward, or if there's anything else I should do :)

[carmocca]

Tests are failing. They need to be fixed

FAILED loggers/test_all.py::test_loggers_fit_test_all[NeptuneLogger] - AttributeError: 'NoneType' object has no attribute 'from_stream'
FAILED loggers/test_neptune.py::TestNeptuneLogger::test_after_save_checkpoint - FileNotFoundError: [Errno 2] No such file or directory: 'path/to/models/last'
FAILED loggers/test_neptune.py::TestNeptuneLogger::test_neptune_leave_open_experiment_after_fit - AttributeError: 'NoneType' object has no attribute 'from_stream'
FAILED loggers/test_neptune.py::TestNeptuneLogger::test_neptune_log_metrics_on_trained_model - AttributeError: 'NoneType' object has no attribute 'from_stream'

[AleksanderWWW]

@carmocca I think I fixed the tests (they pass locally at least), but the pre-commit failure I see now doesn't seem to have anything to do with my changes and they only appeared after I merged the master branch.

[carmocca]

LGTM

cc @Blaizzy for a final stamp from Neptune