DynamoDB on-demand pricing is stale (2x too high) - fix in #932

[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:

• engineering-team/skills/aws-solution-architect/references/service_selection.md

Fix: #932

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