Add documentation page to help user to size a cluster

[fmassot]

Several users can struggle to set the right resources for indexers and other components and choose the right number of indexers/searchers for a given ingestion throughput.

We should add a page with some guidelines. We could start very simply, as having something is always better than nothing.

Some idea:

• One indexer max throughput is around 20MB/s et 40MB/s for 4vCPU and 10GB of memory.
• For an indexer with a Kafka data source, use 100GB of ephemeral storage
• For an indexer receiving ingest requests on the ingest API, targeting EBS of 100GB should be enough.
• and more