(fix): handle `allow-mulitple` query parameter validation

[dsinghvi]

Goal

allow-multiple query parameters should support list examples.

Approach

Validating examples in Fern is pretty complex. So the way I approached this was to validate the query param as a list and as a non-list. If there are no errors in one of the two cases, then fern check passes.

If there are errors, then we list them for the non-list case.