[CNG] [Spike] Consider only building UBI-based images

Context

I believe it was briefly discussed at one point to only build UBI-based images, removing our Debian-based images.

Whether or not this makes sense to do, I wanted to create this issue to capture the benefits and costs and the ultimate decision for posterity.

Some benefits off the top of my head:

• Greatly simplified CNG project and pipelines
• Avoid issues like https://gitlab.com/gitlab-org/cloud-native/gitlab-operator/-/issues/421 where the Operator needs to be aware of installation from OpenShift to prioritize UBI images over Debian-based images (because it could simply always deploy UBI images)
• Others?

Some costs off the top of my head:

• Dependence on a RedHat-provided image (although I don't think we can get around this anyway, as it's required for certain environments)
• Others?

Aggregated answers

Why we should keep shipping Debian

1. Track record, precedent
2. Familiarity of commands
3. Community vs "enterprise" (viewpoint of consumers)

Why we should keep shipping UBI

1. Required in some customer environments
2. Required for RHEL certification and inclusion into the OpenShift Marketplace / RedHat Catalog.

Why we should ship UBI only

1. Simpler pipelines
2. Operator can always ship UBI images instead of only when shipped from RedHat OpenShift Marketplace

We we shouldn't ship UBI only

1. Too vendor-specific
2. Slower-than-desired release cycle