Document what "beta" and "experimental" actually mean, beyond the customer-facing support explanation doc

Created by: Joelkw

This captured what customers could expect but doesn't convey what for and why we use words like "Beta." As code insights approaches beta, we've been getting more questions and confusion as to what that actually means and how it's different conceptually from a prototype.

Clarifying note: we decided to align on "experimental" instead of "prototype." The product team will be making the cascading updates as we can to align here – I'm aware the docs page I link to above says "prototype" as of now.