v0.13.1 Cache environment targets

A performance issue we encountered involved requesting environments that do not exist in a particular SHA. This would result in a cache miss and a lock to verify if the environment was present in the git repo. With this change we now do a lookup for the environment in the environment listing before checking for the environment in the configuration cache. This allows us to respond very quickly with a 404 when the environment does not exist (and can never exist) within the requested SHA.

We have also added in the cache layering from the main branch and recurring db cleanup. The default cache TTL is 90 days. and cleanup will be run once every 24 hours. TTL can be configured using the --db-max-age parameter.