The biggest hold-up was missing fields (`premium_tier`,
`welcome_screen`, etc.) but it looks like someone has provided a
helpful function called `createGuild(...)` to provide sensible default
values.

This commit fixes the errors related to creating a guild from a
template. I've also refactored the code to include roles and channels in
the template.

To make sure that the @everyone role is cloned correctly, when
creating the guild from a template, we check if the role's ID
matches the template's `source_guild_id`. If it does, we set the
@everyone role to the new guild's ID.