Use ubi-minimal image

[tjmoore4]

Checklist:

• Have you added an explanation of what your changes do and why you'd like them to be included?
• Have you updated or added documentation for the change, as applicable?
• Have you tested your changes on all related environments with successful results, as applicable?
  • Have you added automated tests?

Type of Changes:

• New feature
• Bug fix
• Documentation
• Testing enhancement
• Other

What is the new behavior (if this is a feature change)?

• Breaking change (fix or feature that would cause existing functionality to change)
  Updates the postgres-operator image to use ubi-minimal.

Other Information:
Issue: PGO-923