Integrate and schedule CI for Assertoor testing

### Problem description

Ensuring our commits don't break important functionality is always a problem. Having something that can do it for us automatically is useful for ensuring stability.

### Solution description

Integrate [Assertoor](https://ethpandaops.io/posts/assertoor-introduction/) into our CI and have it do daily runs to ensure we didn't break anything in `unstable`. With it running every 24 hours we will be able to determine where things would have broke.

### Additional context

_No response_

Start by reading the linked Assertoor introduction and inspecting Lodestar's existing CI configuration. Determine how Assertoor should run against unstable on a 24-hour schedule, then verify that the scheduled run executes successfully and detects regressions.

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