Support `*.config` (without explicit extension)

[pi0]

Describe the feature

Just an idea while was making this c12 could support configs with any format to be written in foo.config files.

Supporting implicit extensions has downsides, first to say:

• IDEs don't know how to parse it unless it is predefined for them
• Explicit extensions are not clear

On the other hands, c12 can give a powerful thing to support a lot of extensions with 2 try catches (load via mdbox -> jiti) which is not expensive.