This makes sure that all processes that fork off the master have a fully
operation schema cache.
In Rails 6, schema cache is now bolted to the connection pool. This change
ensures the cache on all pools is fully populated prior to forking.
The bolting of cache to connection pool does lead to some strange cases
where a connection can "steal" the cache from another connection, which
can cause stuff to possibly hang or deadlock. This change minimizes the risk
of this happening cause it is already primed.
We make a STRONG assumption that the schema is always the same on all sites
when we spin up a multisite cluster.