Add thiserror instead of exposing eyre anonymous errors

The change here is to make it easier for the consumer to debug the api.
Such that they can `match` on individual errors instead of having to
parse text.

eyre is convenient, but mostly from a consumers perspective

crates/dagger-core/src/gql_client.rs

@@ -15,7 +15,7 @@ pub struct GraphQLError {
 #[derive(Deserialize, Debug, Clone)]
 #[allow(dead_code)]
 pub struct GraphQLErrorMessage {
-    message: String,
+    pub message: String,
     locations: Option<Vec<GraphQLErrorLocation>>,
     extensions: Option<HashMap<String, String>>,
     path: Option<Vec<GraphQLErrorPathParam>>,