Ability to use preexisting postgres server with infisical-standalone helm chart

[mpsOxygen]

Feature description

I would like the ability to not only disable the installation of the postgres helm chart, but also be able to specify a secret from where to get an preexisting postgres server URI.

Why would it be useful?

This would be useful when you don't want to install postgres along with infisical because you already have an existing postgres instance.

Additional context

The existing postgres values would look like this:

postgresql:
  enabled: true
  name: "postgresql"
  fullnameOverride: "postgresql"
  auth:
    username: infisical
    password: root
    database: infisicalDB
  useExistingPostgres:
    # -- When this is enabled, postgresql.enabled needs to be false
    enabled: false
    # -- The name from where to get the existing postgresql connection URI
    existingUriSecret:
      # -- The name of the secret that contains the uri
      name: ""
      # -- Secret key name that contains the uri
      key: ""

And in the Deployment and Job template you would have something like this:

          env:
          {{- if .Values.postgresql.useExistingPostgres.enabled }}
          - name: DB_CONNECTION_URI
            valueFrom:
              secretKeyRef:
                name: {{ .Values.postgresql.useExistingPostgres.existingUriSecret.name }}
                key: {{ .Values.postgresql.useExistingPostgres.existingUriSecret.key }}
          {{- end }}