Implement `scan` operation

**User Story**
`dynamo-helper` does not implement DynamoDB scan operation. `DynamoHelper` needs to implement a `scan` method for users to perform scan operation. This method should take `Filter<T>` as input.

Suggested:
`async scan<T>(filter: Filter<T>): Promise<T>`

Although it should be noted that, when scanning different types of record can be in the result,
