Add Filebeat registry to the diagnostics bundle for the control V2 protocol

[rdner]

Describe the enhancement:

It's possible to register a hook in the control protocol V2 so when the agent requests diagnostics from Filebeat it could send some data useful for debugging back to the agent. This should include the Filebeat registry as well.

Describe a specific use case for the enhancement or feature:

We had a few SDHs that were related to the changed inode value of the input file with the same filename. Filebeat gets confused and can ingest lines multiple times. This might happen due to a log rotation strategy or using a network share as a source filesystem. To diagnose this, we need to scan through the registry log file log.json. It can be done, for example, with this tool.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)