During a config reload, we would keep certs in the cache fi they were used  by the next config. If one config uses InternalIssuer and the other uses a public CA, this behavior is problematic / unintuitive, because there is a big difference between private/public CAs.

This change should ensure that internal issuers are considered when deciding whether to keep or evict from the cache during a reload, by making them distinct from each other and certs from public CAs.