Add environment variable to override endpoint_url

[pedrocaseiro]

• This is a feature with version 2.x of the SDK

With boto3 it's possible to specify an AWS_ENDPOINT_URL to override the default one. Wondering if it would be possible to have the same in aws-sdk-js.

[kellertk]

Thank you for posting request here, and our apologies that we’ve been thinking this over for a long time without much forward motion. There are similar requests to implement this feature in a few of the AWS SDKs and the AWS CLI, so in order to coordinate those teams - and hopefully make the discussions a little easier to follow - we’ve created a new issue in aws/aws-sdk here: aws/aws-sdk#229

[tim-finnigan]

I'm going to resolve this as a duplicate of #3236. As mentioned above there is also an issue in the aws-sdk repository for tracking this feature request at a cross-sdk level.