[Elastic Agent] Support Kafka as an output for elastic agent

[nimarezainia]

Describe the enhancement:
Bringing the Elastic Agent more in line with outputs supported by Beats.

Describe a specific use case for the enhancement or feature:

Enable customers who are using beats to send events/logs to a Kafka broker to be able to create the same environment and functionality using the Elastic Agent. Lack of this capability may be an inhibitor for the adoption of Elastic Agent.

[elasticmachine]

Pinging @elastic/agent (Team:Agent)

[tj-delmarco]

What can we do do get the priority changed for implementation?

[elasticmachine]

Pinging @elastic/elastic-agent-control-plane (Team:Elastic-Agent-Control-Plane)

[jlind23]

@nimarezainia @mostlyjason
Do we already have a design done from the UI perspective and from the configuration perspective?
cc @ph

[mostlyjason]

No design or product definition is done yet AFAIK, but Nima might have more context. Looking at the O11y priority list, there quite a few items ahead of this one and its still waiting for PM assignment. We should sync on it when we're ready to move forward with definition.

[jlind23]

Should be fixed by - elastic/elastic-agent-shipper#116