Add otlpmetric Temporality Preference env var

[MadVikingGod]

This adds the OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE from the spec

[codecov]

Codecov Report

Merging #4287 (c02f4f4) into main (e08359f) will increase coverage by 0.0%.
The diff coverage is 100.0%.

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #4287   +/-   ##
=====================================
  Coverage   83.4%   83.4%           
=====================================
  Files        185     185           
  Lines      14332   14359   +27     
=====================================
+ Hits       11958   11983   +25     
- Misses      2147    2149    +2     
  Partials     227     227           

Impacted Files	Coverage Δ
...orters/otlp/otlpmetric/internal/oconf/envconfig.go	92.0% <100.0%> (+2.5%)	⬆️

... and 1 file with indirect coverage changes

[dmathieu]

Should there be tests? (and a changelog)

[MadVikingGod]

Comment from other PR: There is a lack of documentation around what Environment variables are supported. Could we create somewhere that users can find OTEL_EXPORTER_OTLP_METRICS_TEMPORALITY_PREFERENCE?

[MadVikingGod]

For the documentation of the EnvVar there is a lack of documentation of the entire package. I created a PR (#4336) that includes Environment variables documentation. @pellared can that satisfy the documentation ask here?

[pellared]

For the documentation of the EnvVar there is a lack of documentation of the entire package. I created a PR (#4336) that includes Environment variables documentation. @pellared can that satisfy the documentation ask here?

Sure 👍