[VID-1232] Add negotiation id for subscriber signaling offer-answer methods

[brunoribc]

Introducing a field to the offer on the websocket called "negotiationId", it will be an increasing counter, that basically should be echoed back in the answer (Acting like an ACK-kind of field). This is an effort to avoid unneeded/wrong negotiations, and to be able to safe re-send offers from SFU.
Idea is that:

• SFU sends offer X with negID = 1
• Because of some delay (example low bandwidth / no connection) SFU tries resend the offer. negID = 1
• There's an ICE restart, SFU will never send a different offer while still there's no answer from client.
• Finally client receives the two offers, and sees both have same ID, it should only answer 1 ideally, but it can answer both (SFU will ignore the second), and ice restart can proceed from SFU

This is a pre-step on what's needed for decorrelating ICE restart on websocket recovery. For example, if websocket is recovered and SFU sees signaling (offer/answer exchange) is not stable it can just re-send the current offer in case it was lost when the connection dropped.