Update email alerts configuration guide

[phillxnet]

Our existing email notification configuration entry is a little outdated, both in the options presented/explained and the specific example.

• For the fastmail example given, the correct SMTP server would now be:smtp.fastmail.com (not the indicated mail.messagingengine.com).
• Update pic/text to reflect Web-UI clarification re "Sender email" (was Email)
• Missing doc reference for: "Force username for SMTP Authentication
• Missing doc reference for: "SMTP Port"
• Missing doc reference for: "Test current SMTP params" Button.

All missing doc references/pic improvement requirements are due to improvements within the Web-UI since this doc entry was last edited.

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[EDIT]Potentially this guide could be modified to use a https://proton.me/mail account (Proton Free Tier - 150 emails/day limit) for sending. This may be a more familiar option than fastmail. Especially since fastmail do not offer a free light-use account. This would enable folks to specifically setup such an account for this purpose and more easily follow the configuration offered by way of example. It appears from: https://proton.me/mail/pricing that a "proton mail bridge" is required for the free account to be used via IMAP/SMTP.