helm charts: hardcoded dockerhub `postgres:14`

[sgatewood-da]

For multiple charts we use a hardcoded postgres init container:

      initContainers:
        - name: {{ .Release.Name }}-init-sequencer
          image: postgres:14

We probably want to allow specifying your .Values.imageRepo for this postgres image

[SLoeuillet]

14 still sees updates but 2025-09-25 - PostgreSQL 18 Released!