Provide guidance on the expected latency of batch ingestion into profile

Issue in ./help/ingestion/guardrails.md

This guide provides guidance on the latency of data ingestion into the data lake.

It would be helpful if it also provided guidance on the expected latency of data ingestion into the profile store.
It notes the size guardrails for ingestion to profile store, but no guidance on the latency expectations into profile store.

Start with help/ingestion/guardrails.md and review its existing data-lake latency guidance and profile-store size guardrails. Find the authoritative expected latency for batch ingestion into the profile store, then update the guide so that latency expectations are documented alongside the existing guardrails.

Written by the indexing model from the issue text.