Ensure caches are built for block_rewards POST API (#3305)
Ensure caches are built for block_rewards POST API (#3305)

## Issue Addressed

Follow up to https://github.com/sigp/lighthouse/pull/3290 that fixes a caching bug

## Proposed Changes

Build the committee cache for the new `POST /lighthouse/analysis/block_rewards` API. Due to an unusual quirk of the total active balance cache the API endpoint would sometimes fail after loading a state from disk which had a current epoch cache _but not_  a total active balance cache. This PR adds calls to build the caches immediately before they're required, and has been running smoothly with `blockdreamer` the last few days.




sigp/lighthouse,sigp/lighthouse,sigp/lighthouse,sigp/lighthouse