Add AuthenSASL to perl deps; improve email docs

The addition of AuthenSASL seems to be necessary to properly authenticate against an SMTP server. Without this I got errors such as

error with Hydra::Plugin::EmailNotification=HASH(0x6ad0128)->buildFinished: SMTP auth requires MIME::Base64 and Authen::SASL

Created by  Maximilian Bosch  on April 24, 2021
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