Add temporality selector functions

[dprotaso]

From: #7346

This PR exposes the default TemporalitySelector funcs that are used by the OTel env var processing.

The reason to expose these funcs is because there is some discrepancy in various vendor documentation on how to enable these settings using go option args WithTemporalitySelector

https://cloud-native.slack.com/archives/C01NPAXACKT/p1757443233624599

[MrAlias]

Sorry, please ignore. That was the wrong tab 🤦

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 85.5%. Comparing base (ffeeee8) to head (44e5a13).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main   #7434     +/-   ##
=======================================
- Coverage   85.5%   85.5%   -0.1%     
=======================================
  Files        279     279             
  Lines      24725   24711     -14     
=======================================
- Hits       21158   21146     -12     
+ Misses      3188    3186      -2     
  Partials     379     379             

Files with missing lines	Coverage Δ
...pmetric/otlpmetricgrpc/internal/oconf/envconfig.go	96.8% <100.0%> (-0.4%)	⬇️
...pmetric/otlpmetrichttp/internal/oconf/envconfig.go	96.8% <100.0%> (-0.4%)	⬇️
sdk/metric/reader.go	100.0% <100.0%> (ø)

... and 1 file with indirect coverage changes

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[MrAlias]

Please add a changelog entry and tests to cover the added functionality.

[dprotaso]

Do we want a change log for this?

[dmathieu]

Do we want a change log for this?

Yes, please.

[dprotaso]

included tests and a changelog