proxy: v2.150.0 (#6535)

These release features a change to gateway proxies to support endpoint
targets. Previously, only logical services were supported as gateway
targets.

The proxy now sets an informational header, `l5d-proxy-error`, when the
proxy encounters an internal error. This allows proxy-generated error
responses to be distinguished from application-generated error
responses.

HTTP/2 keepalives are no longer configured by the proxy. This resolves
conflicts with some Go gRPC clients & servers (as described in
linkerd/linkerd2#5988).

Finally, the `*_tcp_accept_errors` metrics now include a `target_addr`
label. This improves diagnostics, especially for TLS detection timeouts.

---

* metrics: Fix metrics test code allowing incomplete matches (linkerd/linkerd2-proxy#1146)
* Add `map_stack` to inbound & outbound builders (linkerd/linkerd2-proxy#1148)
* Update linkerd2-proxy-api to v0.2.0 (linkerd/linkerd2-proxy#1152)
* Remove HTTP/2 keepalive configuration (linkerd/linkerd2-proxy#1149)
* metrics: add target_addr label to TCP accept error metrics (linkerd/linkerd2-proxy#1118)
* build(deps): bump codecov/codecov-action from 1.5.2 to 2.0.1 (linkerd/linkerd2-proxy#1153)
* build(deps): bump tokio from 1.8.1 to 1.8.2 (linkerd/linkerd2-proxy#1155)
* app: Set the `l5d-proxy-error` header on synthesized responses (linkerd/linkerd2-proxy#1119)
* Handle profile endpoint in Gateway outbound stack (linkerd/linkerd2-proxy#1157)
* inbound: Reorganize server into smaller stacks (linkerd/linkerd2-proxy#1156)
* error: Replace `Never` with `std::convert::Infallible` (linkerd/linkerd2-proxy#1158)