Minor expansions and clarifications were added in aws-cloud-practiti…

[djeada]

…oner.md to existing answers

1. Expanded the definition of cloud computing with an emphasis on scalability and cost-effectiveness.
2. Clarified how subnets and VPCs operate within a single region.
3. Provided more detail on EBS snapshots and storage behavior.
4. Added brief explanations for instance types and their characteristics.
5. Offered more information on how RI payment options affect cost savings.