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

assigned to @k204237

requested review from @k204206

requested review from @k204230 and removed review request for @k204206

Many of my questions come from the fact that I am having trouble comprehending the rust code. I started consulting the rust book but I must say it'll take me months if not years of practice to mildly catch up with the level of the code. So in general I think it would be a good idea to keep an eye on the doc-strings to at least explain what's going on, although it might be a no-brainer to you.

Also, would it be possible to add an example toml file to the README? With some comments? That'll be great.

I'll try this out tomorrow with our project data.

I tried to run this with the following config: /work/ch1187/freva-regiklim/freva/drs_config.toml

freva-ingest --data-dir /work/bb1203/freva/model/regional --config-dir  /work/ch1187/freva-regiklim/freva 
2022-06-02T17:08:10.183794Z  WARN ingest_dataset{dataset="nukleus" batch_size=1000}: freva::drs::ingest: /work/bb1203/freva/model/regional/nukleus/output/GER-3km/GERICS/ECMWF-ERAINT/evaluation/r1i1p1/GERICS-REMO2015/v1/1hr/clivi/v20201205/clivi_GER-3km_ECMWF-ERAINT_evaluation_r1i1p1_GERICS-REMO2015_v1_1hr_200909010030-200909302330.nc not a valid drs file, skipping:
InvalidCordexPath(InvalidCordexPathError { reason: "Parsing Error: Error { input: \"nukleus/output/GER-3km/GERICS/ECMWF-ERAINT/evaluation/r1i1p1/GERICS-REMO2015/v1/1hr/clivi/v20201205/clivi_GER-3km_ECMWF-ERAINT_evaluation_r1i1p1_GERICS-REMO2015_v1_1hr_200909010030-200909302330.nc\", code: Verify }" })

I don't really understand why this isn't working. Could you check what is wrong?

added 8 commits

• fd835210 - Make `ingest_opts` a ref again
• 727084ee - Add config example to readme
• d2e5949c - Add warn(missing_docs) to drs and fix issues
• d06121f2 - Forgot to make warn(missing_docs) apply to the module
• b4d03d5e - Add docs to the rest of drs
• 607cb64a - Add some actual documentation to `drs`
• ba1687e3 - Rearrange code for handling data-dir
• f92835d9 - Remove the cordex activity and product constraint

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