Consider AWS_ENDPOINT_URL configuration when resolving service endpoints

[Blind-Striker]

Configuring service-specific endpoints allows users to specify a preferred endpoint for API requests, ensuring consistency. This flexibility supports local endpoints, VPC endpoints, and third-party local AWS development environments. Different endpoints can be designated for testing and production environments. The AWS_ENDPOINT_URL environment variable can define an endpoint URL for individual AWS services.

• When AWS_ENDPOINT_URL is set, the LocalStack.NET configuration seems to break; this needs investigation.
• When AWS_ENDPOINT_URL is set, the LocalStack host should be overridden with the value from this variable.