helm: allow configuration of smtp credentials via existing secret

[hendrikheil]

What this PR does

This PR adds three keys to the helm chart values: smtp.existingSecret, smtp.usernameKey and smtp.passwordKey which allows for secure configuration of the smtp integration.

We noticed this, as we wanted to set all integration keys through secrets. We tried to bypass the Helm chart behavior by defining environment variables through env directly. However as we use Argo CD which has to diff the current state with the desired state, it caused issues. Diffing requires environment key names to be unique, in order to properly create a diff, unfortunately. Instead of just not setting any of the environment keys that the chart is currently setting, I opted to just allow setting the smtp credentials through an existing secret, which is how the other integrations handle it too.

I also added the usernameKey to the secret, as we use Postmark for SMTP where the "password" is also the username, so it needs to be in a secret too.

Which issue(s) this PR closes

There is no related existing issue yet.

Checklist

• [ ] Unit, integration, and e2e (if applicable) tests updated
• [ ] Documentation added (or pr:no public docs PR label added if not required)
• [ ] Added the relevant release notes label (see labels prefixed w/ release:). These labels dictate how your PR will show up in the autogenerated release notes.

[CLAassistant]

All committers have signed the CLA.

[github-actions[bot]]

This pull request has been automatically marked as stale because it has not had activity in the last 30 days. It will be closed in 30 days if no further activity occurs. Please feel free to give a status update now, ping for review, or re-open when it's ready. Thank you for your contributions!

[github-actions[bot]]

This pull request has been automatically closed because it has not had activity in the last 30 days. Please feel free to give a status update now, ping for review, or re-open when it's ready. Thank you for your contributions!