Consider the new JSON fields for Tantivy full-text search

[joepio]

Relates to #40 #210

The new 0.17 release of the Tantivy crate features JSON support.

Current situation

Currently, we have a custom way of indexing, which uses individual triples. This has some serious downsides, such as that if a document has multiple hits in various properties (e.g. hit in Title and Desription field), we cannot combine these and increase its weight.

Opportunities:

• Search in all fields, combined
• Remove some code (love it)
• Include full resources (get_resource_extended), which includes members in collections, maybe?

Implementation suggestion

• In server/search.rs, change the add_resource. Instead of iterating over all prop_vals, just index the full JSON-AD.
• The build_schema now needs a json field.
• When searching, boost the name, perhaps only fuzzy that field + description in default UI