Switch to static resource references

[jtescher]

The spec suggests all spans should have an associated Resource. This change switches trace config and span data from Option<Arc<Resource>> to Cow<'static, Resource> and removes Config::with_no_resource to accommodate this requirement.

[codecov]

Codecov Report

Merging #790 (90c28b0) into main (90a70ee) will decrease coverage by 0.0%.
The diff coverage is 75.5%.

❗ Current head 90c28b0 differs from pull request most recent head f121fdf. Consider uploading reports for the commit f121fdf to get more accurate results

@@           Coverage Diff           @@
##            main    #790     +/-   ##
=======================================
- Coverage   70.2%   70.1%   -0.1%     
=======================================
  Files        109     109             
  Lines       9012    8968     -44     
=======================================
- Hits        6330    6295     -35     
+ Misses      2682    2673      -9     

Impacted Files	Coverage Δ
opentelemetry-datadog/src/exporter/mod.rs	24.4% <0.0%> (+0.2%)	⬆️
opentelemetry-jaeger/src/exporter/config/agent.rs	57.4% <ø> (-0.3%)	⬇️
...emetry-jaeger/src/exporter/config/collector/mod.rs	57.9% <ø> (ø)
opentelemetry-zipkin/src/exporter/mod.rs	0.0% <0.0%> (ø)
opentelemetry-sdk/src/resource/mod.rs	92.6% <75.0%> (+<0.1%)	⬆️
opentelemetry-sdk/src/trace/config.rs	23.8% <75.0%> (+1.3%)	⬆️
opentelemetry-datadog/src/exporter/model/mod.rs	77.3% <100.0%> (ø)
...aeger/src/exporter/config/collector/http_client.rs	23.0% <100.0%> (-0.9%)	⬇️
opentelemetry-jaeger/src/exporter/config/mod.rs	75.0% <100.0%> (-8.1%)	⬇️
opentelemetry-sdk/src/export/trace/mod.rs	100.0% <100.0%> (ø)
... and 6 more

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[TommyCpp]

Looks good 👍 Curious how does the benchmark look like

[jtescher]

@TommyCpp I don't think the benchmarks should change all that much as Arc::clone is not all that expensive, but this is more spec compliant and a few nanoseconds faster per span 👍