Make DICOM Json metadata provider a customizable plugin

[mocsharp]

Is your feature request related to a problem? Please describe.
To ingest data from different data providers and different formats, a metadata provider shall be customizable.

E.g.
if data comes from IG and is DICOM, a DICOM metadata provider loads the DICOM JSON objects.
if data comes from Curie with a proprietary data format, a Curie provider is used to load the Curie metadata

Describe the solution you'd like

Allow the workflow request message to include a type for the metadata provider so WM can load the provider on demand.

Describe alternatives you've considered

A list of supported metadata providers can be configured in appsettings.json and have WM determine which one to use.