Update Ash.Gen.Resource, validate relationship type

[matt-savvy]

Description

Recently found that this ash.gen.resource will let you create something with an invalid relationship.

Example

mix ash.gen.resource MyApp.Blog.Post \
    -r belongs-to:author:MyApp.Accounts.User,has_any:comments:MyApp.Blog.Comment

This has two problems:

• belongs-to (kebab-case) instead of belongs_to (snake_case)
• has_any instead of has_many

I would expect this to fail so I can fix the typos, but instead it creates a resource with a relationships block that looks like this:

       relationships do
         belongs - to(:author, MyApp.Accounts.User)
         has_any(:comments, MyApp.Blog.Comment)
       end

Changes

• Update Ash.Gen.Resource, add valid_relationship_type/1 and call in add_relationships_to_resource.

Contributor checklist

Leave anything that you believe does not apply unchecked.

• I accept the AI Policy, or AI was not used in the creation of this PR.
• Bug fixes include regression tests
• Chores
• Documentation changes
• Features include unit/acceptance tests
• Refactoring
• Update dependencies

[zachdaniel]

🚀 Thank you for your contribution! 🚀