[MISP] Support Attributes API

[jamiehynds]

Our MISP integration currently supports the events API to ingest IOC's. However, the original MISP filebeat module supported both the events and attributes API. The events API generally exposes more data, but can lead to increased storage costs for data which users may not necessarily need or want. The attributes API allows for better filtering to ensure users only ingest the IOC's they are interested in.

Can we add support for MISP Attributes as an additional data stream within the MISP integration please?

[elasticmachine]

Pinging @elastic/security-external-integrations (Team:Security-External Integrations)