Kafka metrics support

### What problem are you trying to solve?

HTTP based traffic is only one type of modern applications. Many use message queues such as Kafka. Getting the metrics for consumers/producers/messages are just as critical to application health as requests and responses in HTTP.

### How should the problem be solved?

Implement a Kafka codec that allows the Linkerd proxy to introspect Kafka's protocol and provide metrics for the communications between consumers and producers. This should show up as a CLI command, dashboard and visualization of the topology between message consumers and HTTP actors.

### Related Issues

- #1779

No files, tests, or entry points are identified in the issue. Start by reviewing related issue #1779 and the existing proxy metrics and CLI architecture. Done would require Kafka protocol introspection with consumer, producer, and message metrics exposed through the CLI, dashboard, and consumer-to-HTTP topology visualization.

Written by the indexing model from the issue text.