feat(sdk): implement exporter metrics (#4976)

* feat(sdk): implement exporter metrics

* changelog

* Lint

* All optional

* Fix

* Cleanup

* Update HTTP exporters

* Format

* context manager

* defaults

* Fixes

* Fix merge

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Co-authored-by: Leighton Chen <lechen@microsoft.com>
Co-authored-by: Riccardo Magliocchetti <riccardo.magliocchetti@gmail.com>