reef: cephadm: use importlib.metadata for querying ceph_iscsi's version

[zdover23]

use importlib.metadata for querying ceph_iscsi's version and fallback to pkg_resources. as the former is only available in Python 3.8, while the latter is deprecated.

Refs https://tracker.ceph.com/issues/66201

This commit is functionally equivalent to a Reef-targeted backport of https://github.com/ceph/ceph/pull/57685.

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[zdover23]

From what I can tell recent pushes have just been changing the formatting, so as long as make check passes this LGTM

Thanks, @adk3798. I'm just learning (at the feet of the extremely patient Josh) about how very finicky Python can be in connection to whitespace. I hope that all my... uh... mucking about... hasn't been too much of an inconvenience. Thanks for your forbearance.

[zdover23]

jenkins retest this please

[zdover23]

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[zdover23]

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