feat: `connectionParams` for subscription

[jjangga0214]

Hi!

Thanks for maintaining this cool explorer.

However, I couldn't find how to set connectionParams for subscription.

To my test, Headers in "Headers" tab are only applied to http (Query, Mutattion), not ws(Subscription).

Let me show you an example of configuring connectionParams in Altair.

[kdawgwilk]

With subscriptions coming soonish to federated graphs this issue is going to become a bigger problem and will likely need to be resolved fairly soon