Add specific search fields for bridges

Meskio reported that we have a new 'transport-info' field in the cached-extrainfo: transport-info version=0.1.0 implementation=lyrebird so bridges can report their implementation and version. This is very new an few bridges do provide this information. But it will be nice to have that information in the API to be able to query it.

Would also be nice to be able to search by distributor and transport.