feat: get specific values and keys from metadata

[frazane]

Description

Adds the option to print out a specific part of the metadata from a checkpoint, using dot notation. For instance:

• anemoi-inference metadata <checkpoint> --get config.dataloader prints out the dataloader config
• anemoi-inference metadata <checkpoint> --get provenance_training. (note the dot at the end) prints out the keys at that node in the dictionary tree
• anemoi-inference metadata <checkpoint> --get provenance_training.module_versions prints out the versions of all training dependencies
• anemoi-inference metadata <checkpoint> --get . prints out the top-level keys

Type of Change

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)
• Documentation update

Code Compatibility

• I have performed a self-review of my code

Code Performance and Testing

• I have added tests that prove my fix is effective or that my feature works
• I ran the complete Pytest test suite locally, and they pass

Dependencies

• I have ensured that the code is still pip-installable after the changes and runs
• I have tested that new dependencies themselves are pip-installable.

Documentation

• My code follows the style guidelines of this project
• I have updated the documentation and docstrings to reflect the changes
• I have added comments to my code, particularly in hard-to-understand areas

Additional Notes

Derp. It's part of stdlib

[gmertes]

Thanks for your contribution!