feat: Added SMTP AUTH PLAIN mechanism for mail authentication

[ip-qi]

By default new config is set to AUTH LOGN method which should not break any current email setups..

Description
Explain what you have changed, and why.

Checklist:

• Securely signed commits
• Component(s) with PHPDoc blocks, only if necessary or adds value
• Unit testing, with >80% coverage
• User guide updated
• Conforms to style guide

[mergeable]

Hi there, ip-qi! 👋

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