Error printed in the console upon entering Game Mode for a project with Multiplayer gem enabled

[LB-KacperKapusta]

Describe the bug Entering Game Mode in any level for a project with Multiplayer gem enabled results in the following error being printed in the console: [Error] (System) - Attempting to spawn players on level load failed. No IMultiplayerSpawner found. Ensure one is registered. The issue does not occur for project using Default template.

Steps to reproduce

1. Create a project with Multiplayer gem enabled.
2. Build the project.
3. Open the Editor.
4. Create a new level.
5. Enter Game Mode.

Expected behavior No errors are present in the console.

Actual behavior The described error is printed in the console.

Screenshots/Video

https://user-images.githubusercontent.com/86953659/204546999-ff2689f8-8ce7-46e0-ba37-93e345c0c57f.mp4

Found in Branch Development (a881574)

Desktop/Device

• Device: PC
• OS: Linux
• Version: Ubuntu 20.04.3 LTS
• CPU: AMD Ryzen 5 3600
• GPU: NVIDIA GeForce RTX 2060 SUPER
• Memory: 16GB

[lmbr-pip]

Users are expected to provide a default spawner.

Fix:

• Improve error messaging.
• Look to improve documentation

[AMZN-Gene]

@LB-KacperKapusta a new level component called "Simple Network Player Spawner" has been added to Multiplayer Gem which allows spawning network players without needing to write custom IMultiplayerSpawner c++ code. It's a level component so you must add "Simple Network Player Spawner" to the root entity in the level (not any child entity); this is to keep devs from accidently adding multiple player spawn handlers to the level which would conflict with eachother. The component accepts a network prefab for the player, and a list of spawn points.

Having a fallback player that spawns if one isn't provided would also rock (see #13895)