Add summary support in the OpenCensus bridge

[dashpole]

Fixes #4571

[codecov]

Codecov Report

Merging #4668 (bf8399f) into main (480edcc) will increase coverage by 0.0%.
The diff coverage is 100.0%.

@@          Coverage Diff          @@
##            main   #4668   +/-   ##
=====================================
  Coverage   81.7%   81.8%           
=====================================
  Files        225     225           
  Lines      18044   18087   +43     
=====================================
+ Hits       14752   14796   +44     
  Misses      2994    2994           
+ Partials     298     297    -1     

Files	Coverage Δ
bridge/opencensus/internal/ocmetric/metric.go	97.2% <100.0%> (+0.4%)	⬆️
...dk/metric/metricdata/metricdatatest/comparisons.go	91.8% <100.0%> (+0.4%)	⬆️

... and 1 file with indirect coverage changes