test: add test case to ensure it works with msw graphql link

[neil585456525]

Hi, regarding issue#63
I would like to propose an update to the library about supporting multiple endpoints for GraphQL use cases.

After testing the official msw feature graphql.link, I discovered that this library can already work with this API. As a result, I have added an integration test and made minor UI adjustments to the example settings-form page to provide an example and testing for this use case.

Related source code in msw:

• new graphql handler with endpoint url (code)
• predict request if match current graphql handler (code)

For other considerations like register & unreqister routes based on the path, so far msw set the edpoint property in graphql handler as private. We can not directly access to this attribute (or we just use it and ignore the ts error).
Another possible but hacky way is getting it from parsing header.

Please let me know that which solution you prefer or if you have any other advises.