`IonConnector`: wait for SFU joined

[avxit]

Why we don't wait for sfu.join finish then call this.onjoin? I'm checking if sfu is defined after onjoin, but since sfu.join is async there is no way to know if sfu.join success or not.

https://github.com/pion/ion-sdk-js/blob/1e7603187c89afd15a83c6b8287b03149de42b06/src/ion.ts#L92-L106

[avxit]

Hello @adwpc, what do you think about it? I can help with a PR if it makes sense to you and everyone. Currently I'm patching the library to use in my project.

[saintplaybitorical]

I think it makes sense. Without fully joining the SFU, calls to .publish(stream) are going to throw.

[adwpc]

@avxit Sorry for late. looks good! thanks!
happy to merge this.