feat: add existingSecretName for email password

[fe80]

Hello,

Context: Onepassword operator doesn't allow empty value for a secret key (https://github.com/1Password/onepassword-operator/issues/157). I create an additional secret with empty value, but I can't add a secret name for email_password.

I'm also blocked with the key napalm secret on 4.1.1, but it's look like remove the this chart.