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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[hughcapet]

as it is not used to ghcr build (direct Dockerfile usage), i would make it just postgres-operator for local builds

[hughcapet]

same here for the naming

[hughcapet]

without tag?