proxy: v2.92.0 (#4264)

This release includes a new protocol detection timeout, which prevents
clients from consuming resources indefinitely when they do not send any
data.

Additionally: the proxy's admin endpoint now supports a `/live` endpoint
for liveness checks, and a feature has been added to enrich tracing
metadata from a file of label/values.

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* Add Labels from a path as oc-collector attributes (linkerd/linkerd2-proxy#463)
* Add liveness endpoint to admin server (linkerd/linkerd2-proxy#470)
* docker: Use buildkit for caching (linkerd/linkerd2-proxy#472)
* Makefile: Use STRIP variable with strip as default (linkerd/linkerd2-proxy#475)
* Add checksec to the release process (linkerd/linkerd2-proxy#476)
* Time out protocol detect futures (linkerd/linkerd2-proxy#464)
* Ensure that checksec is executable (linkerd/linkerd2-proxy#477)
* Fix the checksec URL (linkerd/linkerd2-proxy#478)
* Undo hardcoded release version (linkerd/linkerd2-proxy#479)