This is just an example installer.dat that was "generated" by default values during installation (for reference):

postgres/autoinstall install
postgres/db_host 127.0.0.1
postgres/db_port 45432
postgres/db_name openproject
postgres/db_username openproject
postgres/db_password fjbHvUf5NhDwGWf5TrfKIUPjjOXAnbpS
server/autoinstall install
server/variant apache2

server/hostname geochemprojecthub.corp.alsglobal.org
server/server_path_prefix
server/ssl yes
server/ssl_cert /etc/ssl/certs/cert.crt
server/ssl_key /etc/ssl/private/key.key
server/ssl_ca /etc/ssl/certs/ca-chain_bundle.crt
repositories/api-key MNzupMolSCTjsirBViUX0lbHX7zRA209
repositories/svn-install install
repositories/apache-wrapper-token di9tkjIuURRYvdbBQ3zJIkQ9vdroSH2k
repositories/svn-path /var/db/openproject/svn
repositories/git-install install
repositories/git-path /var/db/openproject/git
repositories/git-http-backend /usr/lib/git-core/git-http-backend/
smtp/autoinstall sendmail
smtp/admin_email admin@domain.com
memcached/autoinstall install
postgres/addon_version v1

Some other options:

smtp/autoinstall smtp
smtp/authentication login
smtp/host smtp.domain.com
smtp/port 587
smtp/username admin
smtp/password password
smtp/domain domain.com
smtp/admin_email admin@domain.com