feat: Support sourcing database connection details from Kubernetes Secrets

[ragutsky]

What was changed

Added support for sourcing database connection details (host, port, user, database) from Kubernetes Secrets via a new existingSecretKeys configuration option. This complements the existing existingSecret parameter which previously only supported passwords.

Changes:

• Added existingSecretKeys field to allow mapping Secret keys to connection parameters
• Updated Helm templates to reference Secret values for host, port, user, and database when existingSecretKeys is configured
• Maintained backward compatibility - existing configurations without existingSecretKeys continue to work as before
• Connection details are now sourced from the Kubernetes Secret instead of being hardcoded in values.yaml

Why?

This addresses the feature request for comprehensive Secret-based configuration management beyond just passwords.

Checklist

1. Closes <>

2. How was this tested:
   Added existing_secret_keys_test.go to ensure new values are compatible with existing ones.

3. Any docs updates needed?

Added docs to the following values files:

• charts/temporal/values/values.postgresql.yaml
• charts/temporal/values.yaml