Prepare repo for contract based integration

[sveitser]

We have a lot of history from our earlier integration approaches and it's not sure if keeping the history is worth it.

What we want to keep these changes

• Sovereign sequencer
• Batch poster
• CI
• Nitro upgrades related code
• Espresso finality node

Changes we no longer need

• STF to validate espresso justifications
• Changes to one-step prover
• Chain param changes (validator no longer need to check if they are validating with Espresso)
• Most tests

We could start with the upstream master branch and add the desired changes only. History would still be available in our original branch on github. Advantage is that we are synced with master, but we lose some git history on the working branch.

Alternatively we would remove the changes we no longer need from the integration branch. Advantage is that we keep all the history, it's less work to get started but we aren't synced with upstream master yet.