proxy: v2.101.0 (#4658)

This release primarily features an upgrade of the proxy's underlying
Tokio runtime and its related libraries. We've observed lower latencies
in initial benchmarks, but further testing and burn-in is warranted.

Also, the proxy now honors the `LINKERD_PROXY_LOG_FORMAT=json`
configuration to enable JSON-formatted logging.

---

* Add a CODEOWNERS (linkerd/linkerd2-proxy#558)
* Fix shellcheck issues in shell scripts (linkerd/linkerd2-proxy#554)
* update the proxy to use std::future and Tokio 0.2 (linkerd/linkerd2-proxy#568)
* Prune unused dependencies (linkerd/linkerd2-proxy#569)
* Support LINKERD_PROXY_LOG_FORMAT=json (linkerd/linkerd2-proxy#500)
* Change docs references from "master" to "main" (linkerd/linkerd2-proxy#571)
* Upgrade tokio-rustls & webpki. (linkerd/linkerd2-proxy#570)
* Makefile: Add shellcheck recipe (linkerd/linkerd2-proxy#555)
* Update proxy-api dependencies (linkerd/linkerd2-proxy#573)
* integration: fix missing traces (linkerd/linkerd2-proxy#572)
* Update Rust to 1.44.0 (linkerd/linkerd2-proxy#574)
* Use async/await to simplify connection-accept task (linkerd/linkerd2-proxy#575)
* Update Rust to 1.44.1 (linkerd/linkerd2-proxy#576)
* outbound: Split HTTP endpoint builder (linkerd/linkerd2-proxy#578)
* Simplify protocol detection with async/await (linkerd/linkerd2-proxy#577)
* Pin proxy-api at v0.1.13 (linkerd/linkerd2-proxy#579)