This implements the metastore for AWS dynamodb.

1. I have implemented most of the configuration options for DynamoDB based on your URL specification in https://mosuka.github.io/phalanx/lock_store.html
2. I have added integration tests using the infrastructure / tooling in the project
3. All the operations are "safe" for create / read and delete, there is currently no update. I added some generic errors to help with this.

So some feedback on the storage interface, I don't think the context.Context or logger should be stored in the DynamodbStorage struct, i think each call should pass the ctx in and the logger should be pulled from the context. This would enable integration of tracing later on, with the ctx propagated all the way through the service.

Need to work out how you want tests added, i have used github.com/ory/dockertest to enable use of dynamodb local inside a test, but this can also just be run with docker-compose or just started locally before running integration tests.