Ability to set config values at runtime

[dead10ck]

Describe your feature request

Hello, I am new to Helix, so please forgive me if I've missed something, but I can't find a command that lets you change config values at runtime, similar to the set command in kakoune and vim. This would be extremely useful for trying out settings, setting file types for undetected files, and generally lots of things that you wouldn't necessarily want to make permanent in your config file. Kakoune's config model with the different scopes is, in my opinion, particularly well designed, and it would be cool to see something analogous for Helix.