Set premium_tier to 0 when creating guild from template

I think we'll need to discuss the proper way to provide default values
here. `premium_tier` for example should never be provided from the
template so it's fine going after the spread operator.

This commit still doesn't allow guilds to be created from template
because the next error is that `welcome_screen` doesn't exist. Our
options:

1. Provide default values in the ORM
2. Provide default values in the guild creation process
3. Throw an error if the template is missing values

Resolves: #1283 but creates a new issue

src/api/routes/guilds/templates/index.ts

@@ -145,6 +145,7 @@ router.post(
 			...template.serialized_source_guild,
 			id: guild_id,
 			owner_id: req.user_id,
+			premium_tier: 0,
 		}).save();
 
 		await Role.create({