Add ingest-stats API

[mmguero]

Document Ingest Statistics

GET - /mapi/ingest-stats

Executes an OpenSearch bucket aggregation query for the host.name field and its maximum (i.e., most regent) event.ingested UTC time value for all of Malcolm's indexed network traffic metadata.

This can be used to know the most recent time a log was indexed for each network sensor.

Example output:

{
  "malcolm": "2024-11-04T14:58:57+00:00",
  "sensor_a": "2024-11-04T14:57:41+00:00",
  "sensor_b": "2024-11-04T14:58:59+00:00"
}

[mmguero]

Needed for #11