CLI plugins

[avaldebe]

add commands and sub-commands from plugin packages using the package metadata

https://packaging.python.org/en/latest/guides/creating-and-discovering-plugins/#using-package-metadata

[avaldebe]

I have a follow up PR that adds a command to just download the metadata and create an extract with only the relevant metadata to the observation files found on a particular directory.
It uses polars to read the metadata CSV and observation Parquet files.
I'll convert the code I'm testing at work into a CLI plugin so it can be enabled as an optional/extra.

[JohnPaton]

lgtm. What were you planning to use this for?

[avaldebe]

I want to add a catalog feature that index some of the most relevant metadata for the data contained on each parquet file.
These datasets have so many files, that IO becomes relevant when trying to figure out the contents of each file.
Therefore, the catalog simplifies the filtering/selection of observations without opening all the files...