Use index.php?graphql for GraphQL endpoint

[justlevine]

In order to support custom graphql endpoints (and maybe sites without pretty permalinks) we should use the underlying WP query to get the GraphQL endpoint in generatePossibleTypes and getGraphqlEndpoint (i.e /index.php?graphql instead of /graphql).

While this is technically filterable in the app itself with graphqlEndpoint, that filter has no effect on type generation. Also, this approach negates the need for a filter entirely (unless maybe you're mocking endpoint data? is that a thing in the frontend ecosystem?).

[josephfusco]

Thanks for bringing this up!

We have partial support for this right now via https://faustjs.org/docs/plugin-system/filters#graphqlendpoint however that filter is currently only supported by the @faustwp/core package.

Note that this approach could also be used within #1318 to improve the WPGraphQL health check.

[josephfusco]

Closed by #1318. Thanks @justlevine!