Add Summary support to the OTLP exporter

[dashpole]

Fixes open-telemetry/opentelemetry-go-contrib#5296

This adds Summary support to the OTLP exporter. Without this, bridges that produce summary metrics aren't very useful.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 83.8%. Comparing base (32e3a3d) to head (eea7a1d).

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #5100   +/-   ##
=====================================
  Coverage   83.8%   83.8%           
=====================================
  Files        248     248           
  Lines      16147   16201   +54     
=====================================
+ Hits       13535   13589   +54     
  Misses      2324    2324           
  Partials     288     288           

Files	Coverage Δ
...ic/otlpmetricgrpc/internal/transform/metricdata.go	100.0% <100.0%> (ø)
...ic/otlpmetrichttp/internal/transform/metricdata.go	100.0% <100.0%> (ø)