DPROD — Decide whether to define or remove dprod:Protocol (class vs. external reference)

See https://github.com/EKGF/dprod/issues/143

The current DPROD model defines both a dprod:Protocol class and a dprod:protocol property for describing service communication mechanisms, but it is unclear whether the class should be retained. This issue seeks a decision on whether to (A) keep and fully define dprod:Protocol with its own metadata properties and SHACL shape, or (B) remove it and instead reference external URIs or SKOS concepts directly from dprod:protocol.

Clarifying this will ensure consistency, clarity, and maintainability in how protocols are modeled across DPROD. The current approach introduces ambiguity around whether protocols should exist as structured internal entities or as references to external authoritative vocabularies. Resolving this will determine how richly metadata can be expressed, how interoperable the model is with external registries (e.g., IANA, W3C), and how closely DPROD aligns with linked data best practices.