Docs: Update schema for audit_events_instance_external_streaming_destinations and audit_events_instance_streaming_event_type_filters

Andrew Jungrequested to merge
andrew-jung/instance-audit-event-tables-sharding-schemas into master

This MR updates the database documentation for db/docs/audit_events_instance_external_audit_event_destinations.yml.

The schema decision was updated, and this MR reflects that change.

Resolution for issues:

Merge request reports