Read gzipped files.

[ccl-core]

Currently, we don't have a way to read gzipped files.

PR #636 introduces a hack to infer whether a file has to be opened with gzip from its name.

Currently, however, don't have a nice way to express this in the Croissant definition itself.

One option to proceed might be to add the gzip media type to the EncodingFormat attribute of a FileObject by concatenating media types using +:

{
      "@type": "cr:FileObject",
      "@id": "file-object",
      "name": "file-object",
      "contentUrl": "file/path/file.json.gz",
      "encodingFormat": "application/gzip+application/json"
    }

Another option might be to change EncodingFormat to support list of media types: "encodingFormat": ["application/gzip", "application/json"].

Alternatively, and possibly preferably, we could introduce a new cr:compression keyword for FileObjects, which could be used similarly to the compression keyword that is available for read_json and read_csv in pandas.