DynamoDB on-demand pricing is stale (2x too high) - fix in #1854

[LeeroyHannigan]

The DynamoDB on-demand throughput rates in this repo predate the November 1, 2024
price cut, which halved them (announcement). The figures currently overstate on-demand
throughput cost by 2x.

	Listed here	Current
Write request units	$1.25 /M	$0.625 /M
Read request units (strongly consistent)	$0.25 /M	$0.125 /M

Authoritative source, versioned and machine-readable:

https://pricing.us-east-1.amazonaws.com/offers/v1.0/aws/AmazonDynamoDB/current/region_index.json

Affected:

• 02-use-cases/01-conversational-agents/lakehouse-agent/deployment/1-cognito-setup/POST_AUTH_SETUP.md

Fix: #1854

Storage ($0.25/GB-month) and provisioned rates were not affected by the cut and are unchanged in
that PR.