[graphiql] Allow passing header options to legacy WS client

Some time ago, the ability to pass headers from a tab to a websocket client was added in the following PR:
https://github.com/graphql/graphiql/pull/2719

We have a similar use case, but are forced into using a legacy WS client. Is there a way of updating the toolkit to allow the headers to passed to the legacy client in the same way?