[FEATURE-REQUEST] Configurable ID field

**Describe the problem you're proposing to solve**

I have a couple of schemas that don't have the field `id`. Judging by looking at the [templates](https://github.com/aesmail/kaffy/blob/master/lib/kaffy_web/templates/resource/_table.html.eex#L11) it seems like this is not configurable.

**Describe the solution you'd like**

It would be great to configure the name of the id columns somewhere in the resources.

**Describe alternatives you've considered**

For now I can get by by aliasing the Ecto column like this:

```
field :id, :string, source: :uuid
```

I might consider just renaming my ID field, so it's not a high priority ticket.

**Additional context**
Add any other context or screenshots about the feature request here.