Add option of "existingSecret" for oneuptimeSecret and encryptionSecret

[luisxkimo]

Is your feature request related to a problem? Please describe.

We can't use "external" secrets to add custom values for oneuptimeSecret and encryptionSecret. This makes insecure this secret when we want to upload the helm values file to a repository.

Describe the solution you'd like Like in the configuration of externalPostgres, add to the configuration of the Helm chart to enable use custom existing secret.

Describe alternatives you've considered If I'm right, in _helpers.tpl should be something like this:

- name: ONEUPTIME_SECRET
  {{- if $.Values.oneuptimeSecret }}
  value: {{ $.Values.oneuptimeSecret }}
  {{- else }}

  {{- if $.Values.externalOneuptimeSecret.existingSecret.name }}
  valueFrom:
    secretKeyRef:
        name: {{ printf "%s" $.Values.externalOneuptimeSecret.existingSecret.name }}
        key: {{ $.Values.externalOneuptimeSecret.existingSecret.passwordKey }}
  {{- else }}
  valueFrom:
    secretKeyRef:
      name: {{ printf "%s-%s" $.Release.Name "secrets"  }}
      key: oneuptime-secret
  {{- end }}
  {{- end }}

Same for ENCRYPTION_SECRET

[simlarsen]

This is merged in already. Closing this.