Create an RFC for moving `thv` state into a proper database

[jerm-dro]

This was an outcome of a team retro. To summarize, the current system of storing run configs in files is brittle and has caused repeated pain. To better manage the version of this state, we want to put into a database, so we can use schema / migration tooling.

[jerm-dro]

@JAORMX Picked up some initial work here: https://github.com/stacklok/toolhive-rfcs/pull/41/changes

However, the remaining "how do we migrate runconfigs into sqlite?" remains to be answered.

[JAORMX]

Runconfigs aren't meant to be state though, hence why they're treated differently in that RFC.