Network Scene Manager

**Please explain the suggested feature in detail.**
No need for a Network Scene Manager ... your current implamentaiton assumes NetworkSceneManager is not null

**How exactly does this keep you from releasing your game right now?**
In all of our projects we manage our scenes our selves and have multiple scenes loaded at any given time. Our scenes do not nessisarly translate to a physical location in the game world, each game's specific scene architecutre is unique ... this is not something that a networking tool needs to bother with and especially shouldn't be requiring to have set up.

**Can you suggest a possible solution?**
Dont assume a NetworkSceneManager is present, if its null assume the dev is handling scene management on its own

**Additional context**
Add any other context or screenshots about the feature request here.

--- Original GitHub issue (auto-fetched) ---
Title: Network Scene Manager

Body:
**Please explain the suggested feature in detail.**
No need for a Network Scene Manager ... your current implamentaiton assumes NetworkSceneManager is not null

**How exactly does this keep you from releasing your game right now?**
In all of our projects we manage our scenes our selves and have multiple scenes loaded at any given time. Our scenes do not nessisarly translate to a physical location in the game world, each game's specific scene architecutre is unique ... this is not something that a networking tool needs to bother with and especially shouldn't be requiring to have set up.

**Can you suggest a possible solution?**
Dont assume a NetworkSceneManager is present, if its null assume the dev is handling scene management on its own

**Additional context**
Add any other context or screenshots about the feature request here.
