proxy: v2.123.0 (#5301)

This release removes a potential panic: it was assumed that looking up a
socket's peer address was infallible, but in practice this call can
fail when a host is under high load. Now these failures only impact the
connection-level task and not the whole proxy proces.

Also, the `process_cpu_seconds_total` metric is now exposed as a float
so that its value may include fractional seconds with 10ms granularity.

---

* io: Make peer_addr fallible (linkerd/linkerd2-proxy#755)
* metrics: Expose process_cpu_seconds_total as a float (linkerd/linkerd2-proxy#754)

.proxy-version

@@ -1 +1 @@
-v2.122.0
+v2.123.0