Support handler merging

[tanner-equi]

The default behavior when working with Parameters is to have them override unless the value is an object. It would be nice to be able to leverage this to our advantage to do things like override global auth handlers to return errors while not overriding other global handlers.

// preview.tsx

export const parameters = {
  msw: {
    auth: someHandler,
    foo: globalHandler
  }
}

// foo.stories.tsx

export default {
  parameters: {
    auth: someOtherHandler,
    bar: myBarHandler
  }
}

This should be interpreted as:

[globalHandler, someOtherHandler, myBarHandler]

[tanner-equi]

Just kidding! Reading the code, it looks like this works out of the box! Thanks!