Some vars can't be set to allow Non-SSL auth mehanism for SMTP

[ShootGan]

According to this dani-garcia/vaultwarden#3477 I think it should be possibility to left this variables empty.

Possible solution:

in the configmap add:

  {{- if .Values.smtp.authMechanism }}
  SMTP_AUTH_MECHANISM: {{ .Values.smtp.authMechanism | quote }}
  {{- end }}

in the statefulset add:

 {{- if .Values.smtp.username }}
            - name: SMTP_USERNAME
              valueFrom:
                secretKeyRef:
                  name: {{ include "vaultwarden.fullname" . }}
                  key: SMTP_USERNAME
            {{- end }}
            {{- if .Values.smtp.password }}
            - name: SMTP_PASSWORD
              valueFrom:
                secretKeyRef:
                  name: {{ include "vaultwarden.fullname" . }}
                  key: SMTP_PASSWORD
            {{- end }}

I can prepare a pull request with these changes.

[guerzon]

Thanks for the report @ShootGan.