Sandbox endpoint URL parameter not working
### Issue Description

In a project I'm working on, the Sandbox is hosted in an URL, while the endpoint it should run introspection is in another. After we updated to Apollo v4, we realized there is no `endpoint` parameter when creating Apollo Server, like there used to be with the GraphQL Playground. 

The closest solution I could find to that problem, would be using the `endpoint` URL parameter, as described [here](https://www.apollographql.com/docs/apollo-sandbox#url-parameters), but something is not right. 

When I set our URL to `https://my-url.com/graphql?endpoint=https://my-url.com/graphql/test` I expect the Connection Setting endpoint to be set to `https://my-url.com/graphql/test`.
Instead I get `https://my-url.com/graphql?endpoint=https://my-url.com/graphql/test` in the Connection Setting endpoint. 

Is there a way to achieve a different endpoint then the URL without changing it manually?

### Link to Reproduction

https://codesandbox.io/p/devbox/modest-fermat-gv8lrv

### Reproduction Steps
For some reason, codesandbox is giving error when initializing. Please run `npm run start` from the terminal.
Add `endpoint` URL param to Sandbox and check the endpoint inside Sandbox.