Removed duplicated file extension when uploading model checkpoints with NeptuneLogger

[Raalsky]

What does this PR do?

When uploading model checkpoints with NeptuneLogger, ckpt files are created under some/namespace/model.ckpt (for instance) in metadata. When user downloads the file or explores the UI the filename is constructed in a form <last part of namespace>.<file extension> so in our case it will end up in model.ckpt.ckpt. This PR removes the extension from namespace which would consist of a filename model.ckpt without dupplicated file extension in filenames.

Preview:

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

Old scripts with Neptune loggers will consist of different metadata structure in Neptune.ai. Filenames after download are now the same as source filenames.

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[tchaton]

LGTM !

[kamil-kaczmarek]

@Raalsky
LGTM