catfile: Emit command stats for catfile operations

Follow-up to !5330 (merged).

We currently also do not have great insight into catfile. This patch adds observability that tracks cumulative time spent in the catfile cache per RPC. As well as how many request_(object|info), flush, and read_(object|info) calls were made, and how long they took.

One open question is that of overhead. If may add up if we end up calling this frequently.