fix: add support postgres existingSecret for indexer

[mamirpanah]

PR(Pull Request) Overview

This PR adds support for indexer authentication to postgres database when using existingSecret instead of plain text password.

Changes

• Major feature addition or modification
• Bug fix
• Code improvement
• Documentation update

Description of Changes

When we use postgres sub chart as dabase for indexer and use plain text password every time we update the helm chart config the postgresql sub-chart create a new secret and postgresql will be restarted, to prevent postgresql from restarting we should use existingSecret in the auth section of postgres config, this PR supports using the existing secret for indexer service.

Testing Method

Explain how to test the changes step by step:

1. Navigate to the helm directory.
2. Change the values.yaml file based on your desired configuration, the main config of cvms should be modified by cvmsConfig.monikers and cvmsConfig.chains.
3. Enable the serviceMonitor of indexer and exporter service.
4. Run helm install my-release cvms/helm to install the Helm chart.
5. Verify that the CVMS pods are running and healthy using kubectl get pods.
6. If you want to add metrics endpoints manually, check the services using kubectl get svc.