Separate pipeline for internal/external build and support multi arch

[idanovinda]

The current Postgres operator uses the open-source registry, which has expired. We need to move to zECR for internal use, but internal policy restricts open-source base images

Closes #2970

[zalando-robot]

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[mikkeloscar]

Maybe do this step in delivery.yaml only as it's CDP specific. Or make the --config flag optional and only enabled in delivery.yaml as that is the only difference for CDP.

[mikkeloscar]

This is a very old version of alpine, maybe we can use the latest? container-registry.zalando.net/library/alpine-3 gives the latest 3.x release of alpine.