Fix Tokenserver metrics

[ethowitz]

When tokenserver.disable_syncstorage is set to true, there is no primary application state; the only application state that exists is Tokenserver's, which doesn't store the Metrics object. In the Tokenserver extractors, we're using the Metrics: FromRequest impl to get access to the metrics, which looks at the syncstorage application state. To resolve this, we'll either want to manually reach into the Tokenserver application state or create a wrapper type around the metrics so we can impl FromRequest specifically for Tokenserver's metrics object.