[NOT TO MERGE] Integrate Beefy into the demo node

[AmbientTea]

Description

Changes required to integrate Beefy into our demo node. Most of these changes were done by @Klapeyron over several months of researching Beefy. I mostly cleaned up the branch and debugged it on local env.

This PR is mostly meant as a showcase and a reminder this topic exists. It should not be merged, because there's still some unresolved issues around backwards compatibility. Namely:

• The SessionKeys type breaks compatibility so upgrading and existing chain to to this version breaks it
• We don't have a tested set of steps to perform an upgrade

Checklist

• Commit sequence broadly makes sense and commits have useful messages.
• The size limit of 400 LOC isn't needlessly exceeded
• The PR refers to a JIRA ticket (if one exists)
• New tests are added if needed and existing tests are updated.
• New code is documented and existing documentation is updated.
• Relevant logging and metrics added
• Any changes are noted in the changelog.md for affected crate
• Self-reviewed the diff