* Explicitly define `mode` in relevant tasks.
* Explicitly define the `nginx` `apt_repository` filename in Debian based distros.
* Building OpenSSL from source should now work properly in CentOS 8.
* Added variable nginx_plus_linux_families: ['Alpine', 'Debian', 'RedHat', 'Suse']
* Added variable nginx_plus_bsd_systems: ['FreeBSD']
* Added variable nginx_freebsd_extra_packages: ['security/ca_root_nss']
* Installation of Linux moved to install-plus-linux.yml
* Installation of FreeBSD moved to install-plus-bsd.yml
* Installation of nginx_freebsd_extra_packages moved to tasks/prerequisites/setup-freebsd.yml
* Installation of NGINX Plus tested with FreeBSD 12.0; Lint passed