New port: mail/roundcube-identity_smtp

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Summary

Roundcube plugin to setup different SMTP settings per identity

WWW: https://github.com/deflomu/Roundcube-SMTP-per-Identity-Plugin

Approved by: ? (mentor)

Test Plan

• portlint -AC looks fine except for false positive warnings
• testbuild by poudriere @11.2-RELEASE finishes fine
• confirmed I can send emails via smtp.freebsd.org from my roundcube server with this plugin