Add registry keyword argument to PrometheusMetricReader (#5055)

* Add registry keyword argument to PrometheusMetricReader

* Fix lint, formatting, and changelog for PrometheusMetricReader registry kwarg

* Apply suggestions from code review

Co-authored-by: Mike Goldsmith <goldsmith.mike@gmail.com>

* Fix CollectorRegistry import and test assertion

* Fix ruff formatting

* fix: convert CRLF to LF in test file

* Fix ruff formatting

* Update exporter/opentelemetry-exporter-prometheus/src/opentelemetry/exporter/prometheus/__init__.py

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Co-authored-by: Mike Goldsmith <goldsmith.mike@gmail.com>
Co-authored-by: Aaron Abbott <aaronabbott@google.com>