Support generated root query for async-graphql

[chipsenkbeil]

Rather than having to hand-write all of the methods for the async-graphql query, it would be nice if we could use something like inventory leveraging ctor or the alternative linkme.

This would need to support compile-time usage of one of these in order to gather all of the defined instances and then gather them into a single query using a macro. Not sure if this is possible right now.

[chipsenkbeil]

Instead of doing the above, a simpler way would to be to support an attribute macro on the impl block of a graphql struct.

pub struct Query;

#[async_graphql::Object]
impl Query {
    // ...
}

would instead become

pub struct Query;

#[entity_async_graphql::query(
    Page,
    BlockElement,
)]
impl Query {
    // ...
}

Need to figure out how to account for diff between enum & struct types as well as handling lifetimes.