feat: Add support for GraphQL federation

[zacharycarter]

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Is your feature request related to a problem? Please describe.

Currently, GraphQL schemas generated with ash_graphql don't support the GraphQL federation specification.

Describe the solution you'd like

Support GraphQL federation through ash_graphql via absinthe_federation.

Describe alternatives you've considered

I've considered using Ash without the ash_graphql extension and then relying on absinthe, but it feels hacky and I'd much prefer the declarative approach Ash GraphQL brings to the table for generating our federated GraphQL schemas.

Additional context

No response

[zachdaniel]

Open to it, PRs welcome 😄