Colectica/ddiregistry: Update to cross platform dotnet core

The DDI Agency Registry is a component of a free global unique identifier system for metadata producing organizations. The registry system provides an agency identifier which acts as both a namespace in a globally unique id as well as a pointer for distributed service resolution. Based on ISO/IEC 11179 Part 6 International Registration Data Identifiers (11179 IRDIs), DDI agency identifiers are used as the Registration Authority (11179 RA) in a IRDI and in DDI URNs.

The DDI Agency Resolver is a free DNS SRV record-based resolution service for DDI agency identifiers, and enables discovery of web services and data services provided by an agency.