crs has no prefix?

mcf uses a plain number for crs at https://github.com/geopython/pygeometa/blob/335e1b87ebbc7decd0c930297b6bb589bbf14f23/sample.yml#L54

this probably assumes the epsg: prefix, but what happens if a crs uses a different prefix? like esri: crs:

wouldn't it be better to allow a prefix, and assume 'epsg:' if none is given (backwards compat)

this actually contradicts the schema, which indicates a full uri as default value
https://github.com/geopython/pygeometa/blob/4c20962cc25a6b00f1ade7926d5fd6aa4354929d/pygeometa/schemas/mcf/core.yaml#L250