Add set_attributes method for Span

[srikanthccv]

This adds the convenience method set_attributes for set multiple attributes.

[codecov]

Codecov Report

Merging #638 (9797bbe) into main (a474268) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main    #638   +/-   ##
=====================================
  Coverage   69.8%   69.9%           
=====================================
  Files        109     109           
  Lines       8912    8927   +15     
=====================================
+ Hits        6226    6240   +14     
- Misses      2686    2687    +1     

Impacted Files	Coverage Δ
opentelemetry-api/src/trace/context.rs	46.4% <ø> (ø)
opentelemetry-api/src/trace/span.rs	100.0% <100.0%> (ø)
opentelemetry-sdk/src/trace/span.rs	93.6% <100.0%> (+0.1%)	⬆️
opentelemetry-sdk/src/metrics/controllers/push.rs	80.0% <0.0%> (-3.4%)	⬇️
opentelemetry-otlp/src/span.rs	0.0% <0.0%> (ø)

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