Docs feedback: Add example for Proton Mail to Omnibus SMTP Settings

https://docs.gitlab.com/omnibus/settings/smtp.html

Addition for Proton Mail (SMTP-Token)

The following section does work with Proton Mail https://proton.me/support/smtp-submission

gitlab_rails['gitlab_email_enabled'] = true
gitlab_rails['smtp_address'] = "smtp.protonmail.ch"
gitlab_rails['smtp_port'] = 587
gitlab_rails['smtp_authentication'] = "plain"
gitlab_rails['smtp_enable_starttls_auto'] = true
gitlab_rails['smtp_user_name'] = "<your email>"
gitlab_rails['smtp_password'] = "<your token>"
gitlab_rails['smtp_domain'] = "<your domain>"
gitlab_rails['gitlab_email_from'] = "<your email>"
gitlab_rails['gitlab_email_reply_to'] = "<your email>"```

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Implementation Guide

Page to add these to: https://gitlab.com/gitlab-org/omnibus-gitlab/-/blob/master/doc/settings/smtp.md