Add dropped attribute counts to events and links

[jtescher]

No description provided.

[jtescher]

@TommyCpp was looking at the proto and it looks like it needs drop counts per event/link. This seem like the best approach? or given the count requirements there you think there may be a better approach?

[codecov]

Codecov Report

Merging #529 (eabc9d3) into main (d3a9dfb) will decrease coverage by 0.0%.
The diff coverage is 64.7%.

@@           Coverage Diff           @@
##            main    #529     +/-   ##
=======================================
- Coverage   52.3%   52.2%   -0.1%     
=======================================
  Files         96      96             
  Lines       8503    8514     +11     
=======================================
+ Hits        4448    4451      +3     
- Misses      4055    4063      +8     

Impacted Files	Coverage Δ
opentelemetry-jaeger/src/exporter/thrift/mod.rs	31.2% <0.0%> (-4.5%)	⬇️
opentelemetry/src/sdk/trace/config.rs	29.0% <8.3%> (ø)
opentelemetry/src/trace/link.rs	60.0% <50.0%> (-13.7%)	⬇️
opentelemetry/src/sdk/trace/span.rs	95.0% <92.8%> (+<0.1%)	⬆️
opentelemetry/src/sdk/trace/tracer.rs	85.8% <100.0%> (+0.1%)	⬆️
opentelemetry/src/testing/trace.rs	63.4% <100.0%> (ø)
opentelemetry/src/trace/event.rs	88.8% <100.0%> (+0.6%)	⬆️
opentelemetry/src/context.rs	92.1% <0.0%> (-0.8%)	⬇️

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[TommyCpp]

This feels like the most natural way to do so. LGTM.
Sorry, I forgot to change the span_limit variable name into plural.