Ingest different DRS formats

This PR is a significant rewrite of how we handle DRS file paths to allow us to ingest paths of a few different known DRS formats.

This involved:

• creating a new crate to handle just loading the different DRS types
• changing ingestion to load the different types and then convert them to our metadata format
• fix some funky issues with data-dir not behaving how it should
  • I also made it optional so not having it means that all datasets are ingested

drs/src/lib.rs

-#[warn(missing_docs)]
+#![warn(missing_docs)]
 pub mod cmip5;
 pub mod cmip6;
 pub mod cordex;