Added example for the ent guide

[Minivera]

The ent guide on the encore.dev website can be difficult to get into due to how specific some of the steps can be. As part of preparing a PR for improving it, I ended up creating a new example project that follows the exact tutorial.

This example shows how to use the ent ORM and could even be used as-is by users wanting to start with an ORM. It also shows the necessary trick of creating an empty migration file.