feat: dynamic prefabs sample

[pdeschain]

This PR adds a new sample to the Basic/ directory
This sample covers the two currently possible use-cases for dynamic prefabs:

• preloading, when all the dynamic prefabs get added on all peers BEFORE we start the connection
• server authoritative dynamic prefab loading - when the server can spawn things that the clients haven't preloaded yet.

Server authoritative dynamic prefab loading can:

• handle late-joiners by ensuring that the client has all the prefabs loaded in connection approval callback
  • the late joining client will load the required prefabs and try again if it's missing any (this potentially could happen several times, if the server adds more prefabs while the client is preloading things)
• it can spawn objects "synchronously" - meaning that the server first ensures that clients have loaded a prefab, and then spawns it, waiting for the clients to ack
• it can spawn objects on the server immediately, marking that object invisible to the clients that haven't loaded the prefab yet (when they do - the server reacts and makes previously hidden objects visible)
• it can ask all the peers to preload prefabs preemptively

Below are the flowcharts for the more complicated spawning strategies that we have: