use Reader to get EDB configmap

[qpdpQ]

What this PR does / why we need it:
Side effect of cache upgrade, because cloud-native-postgresql-operand-images-config doesn't contain watchByCSoperatorLabel we can't use client to get it from cache, use reader instead
Which issue(s) this PR fixes:
Fixes # https://github.ibm.com/IBMPrivateCloud/roadmap/issues/67248

[qpdpQ]

Able to update image in cluster cr

I0725 16:49:25.708449 1 init.go:2636] Postgres Cluster CR common-service-db image is not updated, waiting for update to the desired image in configmap openshift-operators/cloud-native-postgresql-operand-images-config
W0725 16:49:35.683219 1 init.go:2640] Failed to wait for Postgres Cluster CR common-service-db image update: context deadline exceeded
I0725 16:49:35.683286 1 init.go:2642] Updating Postgres Cluster CR common-service-db image to the desired image icr.io/cpopen/edb/postgresql:16.9-5.16.0@sha256:e9e408a13bd103fb46536f896c51e7a27cba38d9b224231b20328a28efe1e616 in configmap openshift-operators/cloud-native-postgresql-operand-images-config
I0725 16:49:35.723754 1 init.go:2653] Postgres Cluster CR common-service-db image successfully updated to the desired image in configmap openshift-operators/cloud-native-postgresql-operand-images-config

IAM operandrequest succeed

[Daniel-Fan]

/lgtm

[ibm-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: Daniel-Fan, qpdpQ

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