Add Cache Status

[ahinkle]

This PR adds a check for the status of the application cache. This check makes sure the application can connect to your cache system and read/write to the cache keys.

Health::checks([
    CacheCheck::new(), // uses the default connection.
    CacheCheck::new()->driver('another-cache-driver'),
]);

[ahinkle]

The failing test is the HTTP ping - not sure what's happening there. 🙂

[freekmurze]

Very nice, thanks! I'll take care of that failing test.