proxy: Update to v2.72.0 (#3447)

This change updates the internals of the proxy's client to the
Destination controller. Other than some minor fixes to the client's
backoff logic, no user-facing changes are expected.

* Split service discovery into composable components (linkerd/linkerd2-proxy#341)
* logging: update `tracing` and `tracing-subscriber` (linkerd/linkerd2-proxy#352)
* resolve: Do not send the 'k8s' scheme (linkerd/linkerd2-proxy#356)

.proxy-version

@@ -1 +1 @@
-v2.71.0
+v2.72.0