Support running bedrock-access-gateway in offline mode (from a PRIVATE_ISOLATED VPC with no NAT Gateway)

[sefinx]

This repo is used together with open webui which is able to run on offline mode. In order to get "full seurity and isolation" we would want to run this from an ISOLATED VPC with VPC enpoint to ECR and Beckdrock. open webui already support this and if bedrock-access-gateway will support this as well it will increase the security level of the solution.