net/xapsd: New port: Apple push notifications daemon for dovecot

Apple push notification daemon for dovecot.

Together with dovecot-xaps-plugin, this will enable push email
for iOS devices that talk to your dovecot IMAP server.

WWW: https://github.com/freswa/dovecot-xaps-daemon

Submitter becomes maintainer. Is already maintainer of other ports.

PR: 269748
Approved by: flo (mentor)
Differential Revision: https://reviews.freebsd.org/D38779