Allow configuring AWS endpoint

Hi,

I'd like to use this library with [Localstack](https://localstack.cloud) to avoid deploying to a real AWS account. Doing so would require overriding the `endpoint` config option for the AWS SDK, e.g.

```ts
const eventBridge = new EventBridge({
endpoint: 'http://localstack_main:4566',
})
```

Would you consider supporting this?