Support tagging/visibility to allow for implementing interest management

[jonbonazza]

A commonly implemented (and in most cases necessary) feature for MMOs is interest management. Essentially, interest management is a way of only broadcasting state updates to players who need to see them in order to reduce bandwidth and processing.

Godot's high-level-multiplayer API allows for implementing such systems via its tagging/visibility feature. As explicitly mentioned in the documentation, Netfox's Synchronizers do no support Godot's visibility features. This makes implementing things like interest management extremely challenging or even impossible.

[annamaria-szentpeteri]

I would like to work on this issue. Please @elementbound assign it to me, if you are okay with it.