main/rrdtool: enable rrd cgi

It's useful for creating tiny webpages with few rrd charts.
(cherry picked from commit 61f0356e)

main/rrdtool/APKBUILD

 # Maintainer: Natanael Copa <ncopa@alpinelinux.org>
 pkgname=rrdtool
 pkgver=1.2.30
-pkgrel=3
+pkgrel=4
 pkgdesc="Data logging and graphing application"
 url="http://www.rrdtool.org"
 license="GPL"