Set default quay-builder image for kubernetesPodman builds

Remove the need for users to set the BUILDER_CONTAINER_IMAGE field and set the default image to registry.redhat.io/quay/quay-builder-rhel8:v3.7.0

Acceptance Criteria

When running builds with the kubernetesPodman executor, removing the BUILDER_CONTAINER_IMAGE field should have the build agents startup using the "registry.redhat.io/quay/quay-builder-rhel8:v3.7.0" image.