[Feat]: allow setting LOWCODER_ADMIN_SMTP_* environment variables in helm chart

[q-gandhart]

I couldn't find a way to set the LOWCODER_ADMIN_SMTP_* environment variables in the helm chart values.yaml file. Since, LOWCODER_ADMIN_SMTP_PASSWORD is a sensitive secret, we should have a secret reference in the values.yaml file to set this value.

something along these lines

global:
  config:
    ...
    admin_smtp_password_secret_ref: foo