fix(argo-cd): fixed externally managed redis secret marked as optional (#2836)

[michaelvl]

Fixes #2836

Note, the settings for Redis in this chart is a little complicated. Generally the options are:

1. External redis (.Values.externalRedis.host)
   • .Values.externalRedis.existingSecret allow naming an external Redis secret
2. Internal redis (if not .Values.externalRedis.host` given)
   • Redis secret hardcoded to argocd-redis
   • If .Values.redisSecretInit.enabled, then Helm chart generates a secret
   • else an externally managed secret is assumed and reference is given with optional: true

The questionable part of this PR is how to make the optional be configurable - especially since there is no good section of the values.yaml file where an option could fit in - the "internal Redis with externally managed secret" does not have a section of its own. Since there are several other references that similarly are given with optional: true my thinking was to create a separate section for 'reference optinality' where other refences could be added in the future. The default values ensures that the change is backward compatible,

Hence, anyone using an externally managed Redis secret will need to add:

configRefOptionality:
  redisUsernameSecret: false
  redisPasswordSecret: false

with this, e.g. the application controller pod will have the following env-var settings:

        - name: REDIS_USERNAME
          valueFrom:
            secretKeyRef:
              name: "argocd-redis"
              key: redis-username
              optional: false.   # <-- note
        - name: REDIS_PASSWORD
          valueFrom:
            secretKeyRef:
              name: "argocd-redis"
              key: auth
              optional: false.   # <--- note

Checklist:

• I have bumped the chart version according to versioning
• I have updated the documentation according to documentation
• I have updated the chart changelog with all the changes that come with this pull request according to changelog.
• Any new values are backwards compatible and/or have sensible default.
• I have signed off all my commits as required by DCO.
• I have created a separate pull request for each chart according to pull requests
• My build is green (troubleshooting builds).