chore: examples/nodejs - adapt code to latest callback and ctx/userData definitions

[Ivansete-status]

NodeJs example adaptation to the latest cbindings approach, where we use a Context and userData.

[NagyZoltanPeter]

Seems all good!
Only remark that we discussed offline.
I see no exact reason for double dereference ctx on the subsequent api calls in C after creation.
I saw that libwaku.nim api procs are waiting for ptr ptr Context while libwaku.h just has the signature void* ctx. This might not be obvious for the lib user from C side to pass a void** ctx. Maybe there is room for future improvement here.
I would consider to use an artificial handle (unique id) as context descriptor not a raw pointer. Such a handle can be checked on the library side to avoid missuse of pointers.

[gabrielmer]

I think that the number of arguments to call a function do not match with the definitions in https://github.com/waku-org/nwaku/blob/c9d558f878f89319ddf397304a475ddb480305cf/library/libwaku.nim for the functions waku_new and waku_set_event_callback

Otherwise LGTM :)