feat: NetworkObjectSpawner for dynamically spawning in-scene placed NetworkObjects [MTT-1558]

[fernando-cortez]

Description

This PR resolves the issue encountered when joining a game session already underway, where the late-joiner would see ghost imps. In-scene placed NetworkObjects were destroyed & despawned on the server, and so the joining client would always load new NetworkObjects which were not synchronized with the server.

Here, NetworkObjectSpawner component can be added to a GameObject inside a scene/prefab to spawn a NetworkObject when NetworkSceneManager's OnLoadEventCompleted is invoked. The wrapper is destroyed after the NetworkObject is spawned inside the server, and otherwise on Awake() on clients, to reduce memory buildup.

Gizmos have been added as a way to at-a-glance spot NetworkObjects in a scene/prefab that will be spawned. I would love to add meshes as a preview, but in my opinion that's more of a nice-to-have, cosmetic, editor tool.

An extra: VandalImpGraphics had an unnecessary NetworkObject added to it which prevented spawns on the entrance area. This has been removed.

Issue Number(s)

MTT-1558

Contribution checklist

• Tests have been added for boss room and/or utilities pack
• Release notes have been added to the project changelog file and/or package changelog file
• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• JIRA ticket ID is in the PR title or at least one commit message
• Include the ticket ID number within the body message of the PR to create a hyperlink

[LPLafontaineB]

Really elegant solution! Something that might be an issue, though, is that now the dynamically-spawned imps are no longer linked to their respective additive scene. So if we move out of it and it gets unloaded, the imps still stay there, but if we come back to it and it gets loaded again, the imps get re-spawned. This means we can have multiple bosses or vandal imps at once