Add methods to collect primary discriptor information from a resource

[chiatt]

Currently modular reports builds the descriptors based on nodes in a report's config:

https://github.com/archesproject/arches-modular-reports/blob/main/arches_modular_reports/src/arches_modular_reports/ModularReport/components/ReportHeader.vue#L42-L70

This spares a trip to the database, however, arches-search needs a default config for search results that will not have any known nodes. For these default node-less configs, we need the descriptor from the resource instance table (at least that seems like the easiest place to get it).