Feature request: per-session config

[just-a-hriday]

Allow individual configuration for different sessions using the session name.
An example use-case: leave the session_restore_mode = "screen" default as is and set session_restore_mode = "simple" for sessions named example-name so that shpool does not interfere with ncurses.

I apologize if this is already possible somehow, but I read through CONFIG.md and config.rs and couldn't find a way to do it.

[ethanpailes]

This seems like a good idea, but might be a bit hard to implement. Not all config settings are session specific, and we'll probably have to re-structure the config somewhat in order to support this approach.

Probably what we would want to do is make a list of config overrides that contain a string regular expressions and then a config object that can be overlaid over the main config when we are in that session. We'd then need to update all our config access points to access config values through a new API parameterized by an Option<Str> session name.