feat: extract client (#48)

This extracts the client (strategy pattern), this is so that it is will be possible to test the actual querier, without hitting / requiring the dagger-engine running.

crates/dagger-core/src/lib.rs

@@ -7,6 +7,7 @@ pub mod config;
 pub mod connect_params;
 pub mod downloader;
 pub mod engine;
+pub mod graphql_client;
 pub mod introspection;
 pub mod logger;
 pub mod schema;