Follow up on AWS deploy docs code block formatting

[tembo]

Follow-up from review on PR #571.

Context: the AWS self-hosted deploy guide includes an AWS Account ID bullet where the aws sts get-caller-identity --query Account --output text command should be moved onto its own nested code block. This can be pushed to a later cleanup pass.

Checklist:

• Update the AWS Account ID bullet in features/self-hosted/deploy/aws.mdx so the AWS CLI command appears as a nested code block.
• Review the state of code blocks throughout the docs site for consistency and readability.