Add pkgbase UCL metadata for `pkgconf`

[ngie]

Summary

This file is needed in order for pkgconf to be installed with pkgbase.
This in turn helps fix make update-packages after pkgconf's introduction
into the base system.

Fixes: a3cefe7f2b4df0f70ff92d4570ce18e517af43ec ("Add 'contrib/pkgconf/' ...")

Test Plan

• make update-packages passes with this change.
• The pkgconf-related packages are produced on my system after running make update-packages:

% for f in /usr/obj/usr/src/repo/FreeBSD:16:amd64/*/FreeBSD-pkgconf*.pkg ; do echo "# $f... "; tar tvzf $f; done
# /usr/obj/usr/src/repo/FreeBSD:16:amd64/16.snap20260423164818/FreeBSD-pkgconf-16.snap20260423164818.pkg... 
-rw-r--r--  0 root   wheel     526 Jan  1  1970 +COMPACT_MANIFEST
-rw-r--r--  0 root   wheel    2020 Jan  1  1970 +MANIFEST
-r-xr-xr-x  0 root   wheel   16920 Apr 23 16:36 /usr/bin/bomtool
lrwxr-xr-x  0 root   wheel       0 Apr 23 16:36 /usr/bin/pkg-config -> pkgconf
-r-xr-xr-x  0 root   wheel   43728 Apr 23 16:36 /usr/bin/pkgconf
-r--r--r--  0 root   wheel   81864 Apr 23 16:36 /usr/lib/libprivatepkgconf.so.5
-r--r--r--  0 root   wheel    1332 Apr 23 16:36 /usr/share/man/man1/bomtool.1.gz
-r--r--r--  0 root   wheel    5828 Apr 23 16:36 /usr/share/man/man1/pkgconf.1.gz
-r--r--r--  0 root   wheel    2345 Apr 23 16:36 /usr/share/man/man5/pc.5.gz
-r--r--r--  0 root   wheel    1420 Apr 23 16:36 /usr/share/man/man5/pkgconf-personality.5.gz
# /usr/obj/usr/src/repo/FreeBSD:16:amd64/16.snap20260423164818/FreeBSD-pkgconf-dbg-16.snap20260423164818.pkg... 
-rw-r--r--  0 root   wheel     666 Jan  1  1970 +COMPACT_MANIFEST
-rw-r--r--  0 root   wheel    1264 Jan  1  1970 +MANIFEST
-r--r--r--  0 root   wheel   25560 Apr 23 16:36 /usr/lib/debug/usr/bin/bomtool.debug
-r--r--r--  0 root   wheel   43720 Apr 23 16:36 /usr/lib/debug/usr/bin/pkgconf.debug
-r--r--r--  0 root   wheel  202240 Apr 23 16:36 /usr/lib/debug/usr/lib/libprivatepkgconf.so.5.debug
# /usr/obj/usr/src/repo/FreeBSD:16:amd64/16.snap20260423164818/FreeBSD-pkgconf-dev-16.snap20260423164818.pkg... 
-rw-r--r--  0 root   wheel     675 Jan  1  1970 +COMPACT_MANIFEST
-rw-r--r--  0 root   wheel    2357 Jan  1  1970 +MANIFEST
-r--r--r--  0 root   wheel    1245 Apr 23 16:36 /usr/include/private/pkgconf/bsdstubs.h
-r--r--r--  0 root   wheel    2016 Apr 23 16:36 /usr/include/private/pkgconf/iter.h
-r--r--r--  0 root   wheel     599 Apr 23 16:36 /usr/include/private/pkgconf/libpkgconf-api.h
-r--r--r--  0 root   wheel   21302 Apr 23 16:36 /usr/include/private/pkgconf/libpkgconf.h
-r--r--r--  0 root   wheel    1708 Apr 23 16:36 /usr/include/private/pkgconf/stdinc.h
-r--r--r--  0 root   wheel  348548 Apr 23 16:36 /usr/lib/libprivatepkgconf.a
lrwxr-xr-x  0 root   wheel       0 Apr 23 16:36 /usr/lib/libprivatepkgconf.so -> libprivatepkgconf.so.5
-r--r--r--  0 root   wheel    1517 Apr 23 16:36 /usr/share/man/man7/pkg.m4.7.gz
drwxr-xr-x  0 root   wheel       0 Apr 23 16:36 /usr/include/private/pkgconf/

[khorben]

This is already in D56589; which version is best?

[ngie]

Abandoning in favor of D56589.