feat: Add support for local synchronization.

[CharlieDigital]

Use Case

At current, it is not possible to synchronize from a remote DynamoDB to a local instance (e.g. running the local emulator or Docker image) due to how the client connection is constructed.

This functionality can be really useful to create a local copy of a remote DDB for testing and development purposes (or possibly even in a CI pipeline).

Proposal

Reuse the existing command line flag --slave-profile to accept a URL endpoint for the localhost when running in local mode.

This will allow synchronization between a remote DynamoDB instance and a local DynamoDB instance.

Key Changes

• Update the argument processing to detect the local endpoint
• Update the client connection to use the local endpoint
• Update documentation on how to use the local mode.

[ned-kelly]

+1