mail/dovecot24: Add version 2.4.2

Originally packaged by Sad Clouds based on mail/dovecot2, and then
modified by many in wip.

While a separate package, this is logically an update to mail/dovecot2
2.3.21.1.

Packaging changes:

  - \todo Explain dropped patches (one by one, even if very briefly),
    so that a reviewer can be sure each removal is appropriate.
  - \todo Explain why xz is dropped.
  - openssl is no longer optional upstream, so the option is removed

Upstream NEWS:
  
  - ?? wiki no longer included
  - ?? change in installed default configs (beyond actual config changes)

\todo