proxy: v2.89.0 (#4163)

This release builds on changes in the prior release to ensure that
balancers process updates eagerly.

Cache capacity limitations have been removed; and services now fail
eagerly, rather than making all requests wait for the timeout to expire.

Also, a bug was fixed in the way the `LINKERD2_PROXY_LOG` env variable
is parsed.

---

* Introduce a backpressure-propagating buffer (linkerd/linkerd2-proxy#451)
* trace: update tracing-subscriber to 0.2.3 (linkerd/linkerd2-proxy#455)
* timeout: Introduce FailFast, Idle, and Probe middlewares (linkerd/linkerd2-proxy#452)
* cache: Let services self-evict (linkerd/linkerd2-proxy#456)

.proxy-version

@@ -1 +1 @@
-v2.88.0
+v2.89.0