Code Generation

**Problem Description**

I've found `mix phx.gen.auth` to be super helpful. Would be great to have code generation like this for Ash, to help reduce the time for new developers to create a working app.

**Desired Solution**

Maybe the best solution would be somehow tied to the Spark DSL builder. I could imagine passing the code generator a yaml file with an app spec. Maybe even a version control system that allows incremental generation, similar in concept to the migration generator.

**Describe alternatives you've considered**

For my own use, I wrote an Ash generator with tooling provided by `Mix.Generator`. You can see the code [here](https://github.com/andyl/mixtasks).

This is something I wrote fast as a proof of concept. It could be expanded, cleaned up for general distribution. But I think it would be possible for an experienced Ash dev to use the Ash tooling and create something more flexible and powerful.

**Express the feature either with a change to resource syntax, or with a change to the resource interface**

As a new Ash developer, I'm not sure what would be the best approach.

**Additional context**

If anyone has suggestions on the optimal design for Ash Code Generation, post them here!

Start by reviewing the linked mixtasks proof of concept and the roles proposed for Mix.Generator and the Spark DSL builder. Clarify whether the resource syntax or resource interface should drive generation, and resolve the YAML and incremental-generation ideas. Done requires an agreed design and a general-purpose Ash generator scope.

Written by the indexing model from the issue text.