Make Visual Editor accessible when custom Query included in GraphQL Schema

**Is your feature request related to a problem? Please describe.**
I can't edit my schema from Amplify Studio. I have a custom query that's hooked up to a lambda function in my schema [per the docs](https://docs.amplify.aws/cli/graphql/custom-business-logic/#lambda-function-resolver). However it seems that this forces my Data Modeling page into a un-editable text view, instead the usual Visual Editor.

**Describe the solution you'd like**
Allow the visual editor to be used even though a custom query is included.

**Describe alternatives you've considered**
I have to make the changes and push from the CLI, which can take a while, and I can't see a friendly non-code UI of what changes I'm making.

**Additional context**
n/a

Start with Amplify Studio's Data Modeling page and the linked GraphQL custom business logic documentation. Reproduce the schema behavior with a custom query backed by a Lambda function, then determine how the Visual Editor handles that schema. Done means users can edit the data model visually while retaining the custom query and its resolver.

Written by the indexing model from the issue text.