Capturing confidence levels from the side of the registry

[matentzn]

We should start thinking about capturing confidence in mappings from the side of the registry.

My suggestion is to have a separate element on the registry if the referenced mapping sets:

mapping_set_id: x:y
registry_confidence: 0.5

which capture how much we "trust" a mapping set. We can specify also a default_registry_confidence directly for the registry metadata, which captures the confidence for all registered mapping sets that do not have a registry_confidence value. I would suggest to set it at 0.75 or something similar.