[chain] Add support for Chain/Validator-Driven Transactions

[patrick-ogrady]

At the end of each block, we should make it possible for a validator to add "unauthenticated" actions. The rules for which/how often actions can be issued (like Oracle updates) can be governed by genesis.Rules.

[github-actions]

This issue has become stale because it has been open 60 days with no activity. Adding the lifecycle/frozen label will exempt this issue from future lifecycle events.

[patrick-ogrady]

There is an open discussion about this topic: #933