Fix URL construction when running in Local Zones

[AndrewAsseily]

Issue #:

CLI-2684

Description of changes:

• Fixed URL construction for Local Zone environments by using region directly from IMDS instead of parsing availability zone
• Replicated fix in AWS CLI v2 and verified: manually tested fix on EC2 instance in Local Zone (us-west-2-lax-1) to verify proper URL construction
• Fixed typo in new-change script documentation

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