api: replace StatusCode and message with Status

[jtescher]

The spec defines status as unset, ok, or error with a description. The current api allows for confusion and misuse by providing invalid combinations (e.g. Ok with a description). This change simplifies the api and removes these illegal states by moving the status to be an enum where only the Status::Error case accepts a message.

[codecov]

Codecov Report

Merging #760 (a62ae72) into main (0704793) will decrease coverage by 0.1%.
The diff coverage is 84.6%.

@@           Coverage Diff           @@
##            main    #760     +/-   ##
=======================================
- Coverage   69.8%   69.6%   -0.2%     
=======================================
  Files        109     109             
  Lines       8868    8824     -44     
=======================================
- Hits        6192    6150     -42     
+ Misses      2676    2674      -2     

Impacted Files	Coverage Δ
opentelemetry-api/src/global/trace.rs	35.1% <0.0%> (ø)
opentelemetry-api/src/testing/trace.rs	45.0% <0.0%> (+2.1%)	⬆️
opentelemetry-api/src/trace/context.rs	46.4% <0.0%> (-2.7%)	⬇️
opentelemetry-api/src/trace/mod.rs	70.2% <ø> (ø)
opentelemetry-api/src/trace/noop.rs	66.3% <0.0%> (ø)
opentelemetry-api/src/trace/tracer.rs	61.3% <33.3%> (+0.2%)	⬆️
opentelemetry-datadog/src/exporter/model/v03.rs	87.0% <50.0%> (ø)
opentelemetry-datadog/src/exporter/model/v05.rs	86.4% <50.0%> (ø)
opentelemetry-jaeger/src/exporter/mod.rs	54.2% <95.2%> (-2.7%)	⬇️
opentelemetry-sdk/src/trace/span.rs	93.4% <95.8%> (-0.3%)	⬇️
... and 11 more

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[TommyCpp]

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