net-mgmt/nagios4: Update 4.5.1 => 4.5.11, take maintainership

Changelog:
https://www.nagios.org/projects/nagios-core/4x/

Improve port:

• Replace PORTVERSION with DISTVERSION.
• Parametrize nagios with ${PORTNAME}.
• Replace CFLAGS, CPPFLAGS and LIBS with USES+=localbase.
• Update CONFLICTS.
• Use ${ETCDIR} instead of ${PREFIX}/etc/nagios.
• Fix warnings from portclippy.
• Fix install with non-default NAGIOSUSER/NAGIOSGROUP.
• Split long line in post-patch.
• Improve indents.
• Regenerate patches with changed line numbers.

PR: 292357
Tested by: Fabian Wenk <fabian@wenks.ch>
MFH: 2026Q1
Co-authored-by: Vladimir Druzenko <vvd@FreeBSD.org>