Add DynamoDB table provisioning hook

[tarqd]

Adds a new example hook (provision-dynamodb-table.sh) that automatically
provisions DynamoDB tables for LaunchDarkly environments with the required
schema (partition key: "namespace", sort key: "key").

Features:

• Automatically creates tables with format ld-{clientsideid}
• Supports both PAY_PER_REQUEST (default) and PROVISIONED billing modes
• Configurable table prefix, capacity, region, and tags
• Checks table existence before creation (idempotent)
• Safe by default: does not delete tables on delete events unless explicitly enabled

Documentation:

• Updated HOOKS.md with configuration options and requirements
• Added README.md example showing basic and advanced usage