Improve behavior for realtime channel creation and improve docs

[jan-tennert]

What kind of change does this PR introduce?

Docs update / Improvement (closes #818)

What is the current behavior?

Calling Realtime#channel() will always create a new channel and override the existing one, if there is one by the given channel id. Also the docs are not very clear.

What is the new behavior?

• Realtime#channel() will now also return an existing channel, if there is one.
• The internal implementation and the docs have also been improved.

[grdsdev]

Hi @jan-tennert this isn't how realtime-js works, on js it can exist multiple channels for the same topic, as its hold by an array.

Tho I do think that the behavior of not having duplicate channels should be the correct, I'm not sure why it is that way, so tagging @filipecabaco for discussion.

[grdsdev]

blocking until correct behavior is discussed

[jan-tennert]

Hi @jan-tennert this isn't how realtime-js works, on js it can exist multiple channels for the same topic, as its hold by an array.

Tho I do think that the behavior of not having duplicate channels should be the correct, I'm not sure why it is that way, so tagging @filipecabaco for discussion.

Yea, I saw that, was actually going to ask about this because the Swift V2 Code also uses a map instead of an array

[grdsdev]

Yes @jan-tennert Swift follows Kotlin's behavior, which is also not aligned with JS.

[filipecabaco]

Swift and Kotlin are more correct. We should do the same on JS as when you subscribe to a topic it should have a "unique" name so this looks like a bug from realtime-js 🤔

[grdsdev]

Approved as Filipe confirmed this is the correct behavior, I'll do the same for Swift.

Just not sure we can do the fix on JS as it seems it will be a breaking change.