Fjord: Failure Modes and Recovery Path Analysis to design docs

This commits adds the public draft version of the FMA for the Fjord hardfork.

Description

We want to publish our initial draft version for the Fjord FMA and share it as out with other dev teams.
Fjord FMA public doc will be published when we merge this PR.

Tests

Please describe any tests you've added. If you've added no tests, or left important behavior untested, please explain why not. No tests needed

ethereum-optimism / design-docs