Rename ExportKind to Temporality

[jmacd]

The name ExportKind predates the use of Temporality in OTel. Fix the usages here.

[codecov]

Codecov Report

Merging #2272 (b406a64) into main (66fccc0) will not change coverage.
The diff coverage is 88.4%.

@@          Coverage Diff          @@
##            main   #2272   +/-   ##
=====================================
  Coverage   72.5%   72.5%           
=====================================
  Files        168     168           
  Lines      11874   11874           
=====================================
  Hits        8611    8611           
  Misses      3029    3029           
  Partials     234     234           

Impacted Files	Coverage Δ
...tlp/otlpmetric/internal/otlpmetrictest/otlptest.go	0.0% <0.0%> (ø)
sdk/export/metric/temporality_string.go	0.0% <0.0%> (ø)
sdk/metric/controller/controllertest/test.go	100.0% <ø> (ø)
sdk/metric/processor/processortest/test.go	85.5% <85.7%> (ø)
bridge/opencensus/exporter.go	100.0% <100.0%> (ø)
exporters/otlp/otlpmetric/exporter.go	60.6% <100.0%> (ø)
...otlp/otlpmetric/internal/metrictransform/metric.go	79.0% <100.0%> (ø)
exporters/otlp/otlpmetric/options.go	100.0% <100.0%> (ø)
exporters/prometheus/prometheus.go	65.2% <100.0%> (ø)
exporters/stdout/stdoutmetric/metric.go	76.2% <100.0%> (ø)
... and 2 more

[jmacd]

I realized two things:
(1) we've discussed this in the past and as a group we try to spell out "AggregationTemporality".
(2) this goes better as a type named aggregation.Temporality