Fix trace and logging user agent, and add tests

[dashpole]

Fixes #713.

I also discovered that the logging exporter was not overriding {{version}} in user agent.

This adds the user agent to the fixture tests, and adds a test to specifically check that the user_agent config is applied to outgoing requests.

[codecov]

Codecov Report

Merging #714 (7077b62) into main (858780d) will decrease coverage by 0.03%.
The diff coverage is 40.74%.

@@            Coverage Diff             @@
##             main     #714      +/-   ##
==========================================
- Coverage   69.60%   69.58%   -0.03%     
==========================================
  Files          37       38       +1     
  Lines        4728     4754      +26     
==========================================
+ Hits         3291     3308      +17     
- Misses       1289     1299      +10     
+ Partials      148      147       -1     

Files Changed	Coverage Δ
...er/collector/integrationtest/protos/fixtures.pb.go	39.42% <0.00%> (-3.07%)	⬇️
exporter/collector/logs.go	45.35% <0.00%> (-0.13%)	⬇️
...er/collector/integrationtest/inmemoryocexporter.go	87.71% <100.00%> (+0.10%)	⬆️
...lector/integrationtest/testcases/testcases_logs.go	100.00% <100.00%> (ø)
...tor/integrationtest/testcases/testcases_metrics.go	100.00% <100.00%> (ø)
...ctor/integrationtest/testcases/testcases_traces.go	100.00% <100.00%> (ø)
exporter/trace/trace.go	90.16% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[aabmass]

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