www/nginx-prometheus-exporter: Update to 0.9.0

• Redirect stdout/stderr to syslog (1)
• Pet portclippy
• Reformat Makefile with portfmt

ChangeLog: https://github.com/nginxinc/nginx-prometheus-exporter/releases/tag/v0.9.0
PR: 258753
Reported by: bgdnlp <freebsd.org at neant.ro> (1)
Approved by: ygy (mentor)
Differential Revision: https://reviews.freebsd.org/D32547