Update "links.json" with new protocol type

[ESapenaVentura]

For which schema is a change/update being suggested?

I would like to request an update to the links.json schema

What should the change/update be?

I would like to add a new value to the enum of the field definitions.protocol.protocol_type to atone for the new protocol type introduced, treatment_protocol

This update constitutes a minor change to the schema(s) it affects.

Why is the change requested?

This change is needed to be able to ingest the recently approved treatment_protocol