Implement Joins at runtime using DynamoDB Batch APIs

[aruizeac]

Amazon DynamoDB is known as a key-value database with document properties.

Hence, using trivial SQL-functionalities do not come out the box.

In order to make development easier, implement JOIN SQL statements using DynamoDB APIs (Maybe BatchGet API?).

In other words, an mechanism to hydratate related entities of a given document.

In addition, this might require the definition of Models just like any other ORM.

[aruizeac]

Instead calling this feature join. better use hydration.

Added schemas for nodes and edges. Might require to look at ent implementation of graph-oriented schemas.