neptune.init deprecation fix

[wouterzwerink]

What does this PR do?

neptune.init is deprecated. Support will end in neptune-client==1.0.0. neptune.init_run should be used instead.

Fixes #15394

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

None

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[awaelchli]

@wouterzwerink This is a great start, thanks for providing the fix for this. Two more things we need to do:

• Find the version in which init got deprecated. In NeptuneLogger, conditionally use init or init_run depending on whether the installed version is greater or smaller than that.
• We would need to update the init references in tests in tests/tests_pytorch/loggers/test_neptune.py

We can of course help with these items.

[wouterzwerink]

@awaelchli I have updated the references to init in the test files.
neptune-client has marked init as deprecated since neptune-client 0.16.10. However, it seems unnecessary to conditionally use init or init_run, since init_run has been supported (and preferred) since the switch from legacy neptune to neptune.new. It looks to me like lightning does not support the legacy neptune API, so init_run should always work.

[awaelchli]

@wouterzwerink That's really good news. Thanks for checking!