fix: deduplicate imagePullSecrets

Closes #62 (closed)

See linked issue for more details

Currently, BB is using the deprecated value https://repo1.dso.mil/big-bang/bigbang/-/blob/master/chart/templates/sonarqube/values.yaml#L35

This shouldn't affect actual deployments as the default in this chart is set to the same value. However, someone should clean up the default values there to either use the non-deprecated pull secret value, or remove it altogether