Add a new metric to track the number of requests that had their KV blocks
expire. The scenario is particularly important to surface and track as it is a
vital indicator of the health of the deployment.
Currently we're resorting to track these failures through unstructured log
parsing (which is, among other thing, error string dependent); current main:
> Releasing expired KV blocks for request cmpl-071d which were retrieved by 0 decode worker(s) within 0 seconds.
Signed-off-by: NickLucche <nlucches@redhat.com>
758df5afe7