Basic Integration with Datafusion

[marvinlanhenke]

I had some fun, working with Datafusion and I want to share the (rough) design with you.

As outlined in #242 I went ahead and:

• created a new crate integrations
• a subfolder datafusion with its respective modules (catalog.rs, schema.rs, etc.)
• implemented some of the traits e.g. CatalogProvider
• basic test infra for integration test with HiveMetastore

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The overall structure should be extensible, meaning - if we want to support an integration with e.g. polars we simply create a new subfolder and implement the traits.

The test infra is supposed to be used by every integration.

The IcebergCatalogProvider, for example, should be usable by any Catalog (since it Arc for the client (dynamic dispatch))

I really would appreciate your thoughts on this approach - so we can discuss how to proceed, whats missing upstream (like #277), etc.