feat: add pre and post spawn methods [MTT-8470] up-port v2.0.0#2912

NoelStephensUnity merged 14 commits intodevelop-2.0.0Unity-Technologies/com.unity.netcode.gameobjects:develop-2.0.0from

feat/add-pre-and-post-spawn-methods-mtt-8470-up-port-v2-0-0Unity-Technologies/com.unity.netcode.gameobjects:feat/add-pre-and-post-spawn-methods-mtt-8470-up-port-v2-0-0Copy head branch name to clipboard