Update WebSockTransport request header and connectingPayload

[yootsubo]

Addresses #1178

In addition, added a similar functionality to update the connectingPayload.
This is to handle similar use case to #1178 but for those who use the connectingPayload to send the auth token (what my team is currently doing).

[apollo-cla]

@yootsubo: Thank you for submitting a pull request! Before we can merge it, you'll need to sign the Apollo Contributor License Agreement here: https://contribute.apollographql.com/

[designatednerd]

Awesome - any chance you've got a minute to throw some tests on for this?

[gazzer82]

Thanks for doing this, got swamped the last few days!

[yootsubo]

@designatednerd Tests added! Let me know if theres anything else :)

[designatednerd]

Sweet! I might do some stuff tomorrow to have it hit a live websocket on localhost instead of using a mock socket, but this is fantastic. Thanks so much for your help!