Create an audit log of clients using schemas

[harshach]

We should introduce clientId to SchemaRegistryClient which will at configured interval sends a heartbeat to the registry server along with schema id & version it's using and if it's a producer or consumer. This will help us build an audit log of clients accessing schemas. This will in-turn give indications to Schema Authors to see any potential change to schema might affect which clients.

[michaelandrepearce]

+1 I like this idea, very useful.