* Add field event.agent_id_status

This adds a field that can be used to reflect the status of the agent.id verification performed by the receiving system or data pipeline. If the receiving system checks that the sender is authorized for a given agent.id value then the outcome can be added to this field.

For example you might implement mTLS for authenticating agents sending data to Logstash. You could add the agent's ID to the agent's client cert subject and then validate incoming events in your Logstash pipeline to ensure the data has the agent ID.

Or with Elasticsearch you could provide each of your agents with an API key that has the agent.id associated to the API key metadata. Then using an Ingest Node pipeline you can validate the agent.id against the client's API key metadata.

* Shorten value names, remove allowed_values
# Conflicts:
#	experimental/generated/csv/fields.csv
#	generated/csv/fields.csv