[DOCS] Explain tx finality, fault proof window, and sequencer policy

## Brief Description of the Docs Request
New docs page covering the nuances of tx finality, sequencer policy and challenge periods to debunk the belief that OP Stack chains take 7 days for finalization

## Description of the Documentation You'd Like
See here: https://docs.google.com/document/d/1edsf4eFjLcs5t7xIJ2DEYw1grw2yNz9qbeEOWEfYdaQ/edit


