Deprecated pkg resources

[VukW]

pkg_resources is deprecated. Using it breaks gandlf now: while extracting gandlf version, it builds a whole tree of dependencies and fails as torchio requires typer[all], while modern typer==0.12.0+ doesn't have all option anymore (compare to 0.11.1, "Installation" section). Though the issue itself is very minor, pkg_resources treat it as critical and fails. The best solution is just to replace pkg_resources with more modern tools

Proposed Changes

• replace pkg_resources with importlib.metadata to extract gandlf version

Checklist

• [x] CONTRIBUTING guide has been followed.
• [x] PR is based on the current GaNDLF master .
• [x] Non-breaking change (does not break existing functionality): provide as many details as possible for any breaking change.
• [x] Function/class source code documentation added/updated (ensure typing is used to provide type hints, including and not limited to using Optional if a variable has a pre-defined value).
• [x] Code has been blacked for style consistency and linting.
• [x] If applicable, version information has been updated in GANDLF/version.py.
• [x] If adding a git submodule, add to list of exceptions for black styling in pyproject.toml file.
• [x] Usage documentation has been updated, if appropriate.
• [x] Tests added or modified to cover the changes; if coverage is reduced, please give explanation.
• [x] If customized dependency installation is required (i.e., a separate pip install step is needed for PR to be functional), please ensure it is reflected in all the files that control the CI, namely: python-test.yml, and all docker files [1,2,3].

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