proxy: rc.conf.d subdir for squid, only way to merge configs

src/opnsense/scripts/proxy/setup.sh

 #!/bin/sh
 
+# XXX Used to be a flat file, but we need a pluggable
+# XXX directory.  Can safely remove this post-17.1.
+RC_CONF_D="/etc/rc.conf.d/squid"
+if [ -f ${RC_CONF_D} ]; then
+    rm ${RC_CONF_D}
+fi
+
 SQUID_DIRS="/var/log/squid /var/run/squid /var/squid /var/squid/cache /var/squid/ssl /var/squid/logs"
 
 for SQUID_DIR in ${SQUID_DIRS}; do

src/opnsense/service/templates/OPNsense/Proxy/+TARGETS

-rc.conf.d:/etc/rc.conf.d/squid
+rc.conf.d:/etc/rc.conf.d/squid/squid
 squid.conf:/usr/local/etc/squid/squid.conf
 newsyslog.conf:/etc/newsyslog.conf.d/squid
 externalACLs.conf:/usr/local/etc/squid/externalACLs.conf