Support for "in" and "contains" operations for metadata filter queries

[maxnoe]

Description

Imagine custom metadata (e.g. using the JSON backend) like this:

did_client.set_metadata_bulk(scope, name1, meta={"categories": ["foo", "bar"], "format": "fits"})
did_client.set_metadata_bulk(scope, name2, meta={"categories": ["bar", "baz"], "format": "ecsv"})

We'd like to support filters with operations in and contains, i.e. for the list metadata item, querying for contains:

did_client.list_dids(scope, filters={"categories.contains", "bar"})

or "in" for the format:

did_client.list_dids(scope, filters={"format.in", ["fits", "ecsv"]})

The first (contains) is impossible currently I think. The second form is "only" a more concise version of listing multiple dictionaries:

did_client.list_dids(scope, filters=[{"format", "fits"}, {"format": "ecsv"}])

but this format gets unwieldy pretty fast if combined with other conditions.

Motivation

Enabling more complex queries on metadata.

Change

Support for the new operators added to metadata plugins.

[bari12]

Hi @maxnoe this is definitely something we want to do. @Geogouz just started to work on the metadata this month.