Metadata is not documented in JavaScript interoperability guide

[Munksgaard]

The JavaScript interoperability guide does not mention the metadata field, which is mentioned several times in the Bindings guide. It doesn't seem to be the case that it is just passed on to Phoenix.Socket, so I think it should be documented in the javascript interoperability guide as well.

[SteffenDE]

Thank you for reporting!

[Munksgaard]

You're welcome, thanks for the fix ❤️