Add the spawn command

[haykam821]

This pull request adds a command for teleporting players to the lobby spawn, replacing the previous manually-configured aliases:

{
	"aliases": {
		"spawn": {
			"execute": [
				"execute in minecraft:overworld run tp @s 0 66 0 0 0",
				"gamemode adventure"
			],
			"feedback": false
		},
		"hub": "spawn",
		"lobby": "spawn"
	}
}

The equivalent configuration would be:

{
	"lobby_spawn": {
		"pos": [
			0,
			66,
			0
		],
		"game_mode": "adventure"
	}
}

In addition, this command gives players lobby items (the navigator and tater box) so that players do not need to relog if they lost those items.