Integrate OpenTelemetry into the proxy

[sfleen]

OpenCensus is a deprecated protocol and is slated to be removed from upstream collectors soon.

This wires up the proxy to optionally use OpenTelmetry as the format for exported traces. Currently, this defaults to the existing OpenCensus exporter, and we can switch the default later.

#10111

[codecov]

Codecov Report

Attention: Patch coverage is 16.98113% with 176 lines in your changes missing coverage. Please review.

Project coverage is 67.53%. Comparing base (96124bc) to head (673f71f).
Report is 468 commits behind head on main.

Files with missing lines	Patch %	Lines
linkerd/opencensus/src/lib.rs	0.00%	41 Missing ⚠️
linkerd/app/src/trace_collector/otel_collector.rs	0.00%	38 Missing ⚠️
linkerd/opentelemetry/src/lib.rs	0.00%	29 Missing ⚠️
linkerd/app/src/trace_collector.rs	30.00%	21 Missing ⚠️
linkerd/app/core/src/http_tracing.rs	10.00%	18 Missing ⚠️
linkerd/app/src/trace_collector/oc_collector.rs	0.00%	9 Missing ⚠️
linkerd/app/src/lib.rs	72.00%	7 Missing ⚠️
linkerd/trace-context/src/lib.rs	0.00%	7 Missing ⚠️
linkerd/app/src/env.rs	45.45%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3221      +/-   ##
==========================================
- Coverage   67.68%   67.53%   -0.15%     
==========================================
  Files         332      365      +33     
  Lines       15158    16989    +1831     
==========================================
+ Hits        10259    11473    +1214     
- Misses       4899     5516     +617     

Files with missing lines	Coverage Δ
linkerd/app/core/src/lib.rs	87.50% <ø> (ø)
linkerd/app/core/src/metrics.rs	98.46% <100.00%> (+0.02%)	⬆️
linkerd/app/inbound/src/lib.rs	81.69% <ø> (+0.26%)	⬆️
linkerd/app/outbound/src/http/server.rs	60.65% <ø> (-1.42%)	⬇️
linkerd/app/outbound/src/lib.rs	56.96% <ø> (ø)
linkerd/app/src/env/trace.rs	50.00% <ø> (ø)
linkerd/app/src/env.rs	53.14% <45.45%> (-6.26%)	⬇️
linkerd/app/src/lib.rs	87.39% <72.00%> (-1.19%)	⬇️
linkerd/trace-context/src/lib.rs	6.66% <0.00%> (-2.03%)	⬇️
linkerd/app/src/trace_collector/oc_collector.rs	0.00% <0.00%> (ø)
... and 5 more

... and 47 files with indirect coverage changes

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[olix0r]

General shape of this is looking good to me. Some smaller nitty gritty feedback...