[Task] Expose `jvmId` through GraphQL query in target metadata

@maxcao13 in doing this I have just noticed that the jvmId comes through in the HTTP REST API metadata, but it isn’t available to query via GraphQL. Would you mind taking a look at that?

_Originally posted by @andrewazores in https://github.com/cryostatio/cryostat/issues/964#issuecomment-1252439523_

[andrewazores]

The reason I was tinkering around with that ID in the ServiceRef is also related to the comment I made the other day about the new beta API handlers and the /:sourceTarget path param being an ID rather than the JMX service URL. I was experimenting with the -agent generating itself a UUID and including that when it published discovery updates about itself, too. Using the JVM hash ID as the ServiceRef ID for JMX discovery makes a lot of sense, rather than just using a UUID. If I add -core as a dependency to -agent, or if we otherwise make the JVM hash ID function available for use in the -agent, we can also have the agent produce consistent ID results for itself at discovery registration/publish time as what Cryostat would see when connecting to it over JMX.

[andrewazores]

I do think that the ServiceRef is the right place for the ID. I don’t think adding a reference to the jvmIdHelper to the ServiceRef is the best thing to do though. Better to put that wherever the ServiceRefs are instantiated and just pass the ID string in as a constructor parameter to the ServiceRef which holds it as an immutable field.