[kafka Exporter] refactor tests (#16265)
[kafka Exporter] refactor tests (#16265)

These tests needed a little love to make it easier to contribute to the
component

Co-authored-by: Alex Boten <60c6d277a8bd81de7fdde19201bf9c58a3df08f4@boten.ca>
open-telemetry/opentelemetry-collector-contrib,open-telemetry/opentelemetry-collector-contrib