Add jaeger tracing backend support

[haubenr]

Changes

This PR adds Jaeger tracing backend support to the tracing package (in addition to the already existing Zipkin support).
Parts of the code in this PR were taken from an earlier (and seemingly abandoned code change proposed here: #1079

/kind enhancement

Fixes #2561

[knative-prow]

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[codecov]

Codecov Report

Merging #2562 (4152844) into main (3764d73) will decrease coverage by 0.23%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main    #2562      +/-   ##
==========================================
- Coverage   81.61%   81.37%   -0.24%     
==========================================
  Files         163      163              
  Lines        9715     9747      +32     
==========================================
+ Hits         7929     7932       +3     
- Misses       1549     1579      +30     
+ Partials      237      236       -1     

Impacted Files	Coverage Δ
tracing/opencensus.go	37.40% <0.00%> (-12.10%)	⬇️
controller/controller.go	88.78% <0.00%> (+0.71%)	⬆️

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[haubenr]

/test unit-tests_pkg_main

[haubenr]

The Downstream Tekton 'tektoncd/pipeline' fails due to an unrelated issue with the knative.dev/pkg/changeset module where the interface expectation of tekton (wants to receive two return values) is not matched by the actual knative function implementation (returns one value).

[dprotaso]

/hold - see my comment on the issue

[haubenr]

Alright, moving from OpenCensus to OpenTelemetry sound reasonable. I'll close this PR.