Support custom endpoint URLs for AWS provider

This is a Feature Proposal

Description

The AWS CLI supports using --endpoint-url when issuing commands. This feature is useful for overriding the defaults, for example in conjunction with atlassian/localstack for local development.

This would provide additional support for integration testing on a local machine.

For example, if a function receives an SNS event X, performs some processing, and publishes a new SNS event Y, unit testing can test the processing code. However a higher level BDD scenario is not supported:

Scenario: event X
When event X is sent
Then event Y should be created

Similar or dependent issues: This is similar to the Serverless Offline Plugin, but would provide a language agnostic solution.

Additional Data

To run against a custom endpoint you could use:

serverless deploy --endpoint-json file://local-endpoint.json

Where local-endpoint.json contains:

{
    "awslambda": "http://localhost:4574",
    "cloudformation": "http://localhost:4581",
    "dynamodb": "http://localhost:4569",
    "kinesis": "http://localhost:4568",
    "redshift": "http://localhost:4577",
    "route53": "http://localhost:4580",
    "s3": "http://localhost:4572",
    "ses": "http://localhost:4579",
    "sns": "http://localhost:4575",
    "sqs": "http://localhost:4576"
}

[temyers]

I’ve done an initial push to: https://github.com/temyers/serverless-localstack

This is still very much a WIP, and the example isn’t fully working yet.
But I wanted to push to give early visibility.

[gertjvr]

https://github.com/serverless-community-labs/serverless-plugin-simulate supports localstack with a docker-compose file.