feat: remote templates config files

[AlexD10S]

Suggested by @peterwht and @moliholy

Take the templates configuration out of the Pop CLI and store it in an external config file that Pop loads when creating the templates. This way, any updates or fixes can be made without releasing a new version.

This can be even more useful once Frontend templates are introduced in #676 which are expected to evolve more frequently.

This will also close the existing issue #400