Enable configuration of the zstd compression level for feather store

[dispanser]

This came up during work on the parquet / feather benchmarks, where we want to measure the effect of various compression levels for both parquet and feather.

This change follows closely what we do for the parquet plugin to make the zstd compression level configurable.

📝 Reviewer Checklist

Review this pull request by ensuring the following items:

• All user-facing changes have changelog entries
• User-facing changes are reflected on vast.io

[dispanser]

I guess I still need to add a changelog entry, extend vast.yaml.example, and find a place in our documentation to add the parameter.

NB, there is no documentation for parquet plugin configuration options. Where's a good place for that?

[dominiklohmann]

NB, there is no documentation for parquet plugin configuration options. Where's a good place for that?

I'd say under tuning: https://vast.io/docs/setup/tune

[dominiklohmann]

I think this is almost there. Happy to see this lands, especially in light of the data analysis from the recent blog post.

[dominiklohmann]

Just wordsmithing now. I think this is ready to go! 🚀