feature: support local endpoints for SQS and S3.

[0xkalvin]

Description

One common way of setting up a local development environment for AWS services is using Localstack.
In order for that to work, we need a way to point our services endpoints to a local URL that uses HTTP instead of HTTPS.

This PR adds support for passing a local endpoint for SQS and S3.

To manually test this with Localstack:

Start the Localstack container with

docker run --rm -it -p 4566:4566 -p 4571:4571 localstack/localstack

Create a dummy queue and a dummy s3 bucket

aws --endpoint-url=http://localhost:4566  --region=us-east-1 sqs create-queue --queue-name dummyqueue

aws --endpoint-url=http://localhost:4566 s3 mb s3://dummybucket

Run this script

aws.initialize({
  accessKeyId: 'fake_key',
  secretAccessKey: 'fake_secret',
  region: 'us-east-1'
});

const queueName = 'dummyqueue';

const sqs = aws.SQS({
  account: '000000000000',
  bypassProxy: false,
  sqsEndpoint: 'localhost:4566',
  sqsProtocol: 'http',
  s3Endpoint: 'localhost:4566',
  s3Protocol: 'http',
  s3ForcePathStyle: true
});

async function run() {
  const sendMessageResult = await sqs.extendedSend({
    queueName,
    payload: {
      foo: 'bar'
    },
    s3Bucket: 'dummybucket'
  });

  console.log(sendMessageResult);
}

run();