Introduce dnssec-policy configuration

This commit introduces the initial `dnssec-policy` configuration
statement. It has an initial set of options to deal with signature
and key maintenance.

Add some checks to ensure that dnssec-policy is configured at the
right locations, and that policies referenced to in zone statements
actually exist.

Add some checks that when a user adds the new `dnssec-policy`
configuration, it will no longer contain existing DNSSEC
configuration options.  Specifically: `inline-signing`,
`auto-dnssec`, `dnssec-dnskey-kskonly`, `dnssec-secure-to-insecure`,
`update-check-ksk`, `dnssec-update-mode`, `dnskey-sig-validity`,
and `sig-validity-interval`.

Test a good kasp configuration, and some bad configurations.

bin/tests/system/checkconf/good-kasp.conf

@@ -0,0 +1,47 @@
+/*
+ * Copyright (C) Internet Systems Consortium, Inc. ("ISC")
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ *
+ * See the COPYRIGHT file distributed with this work for additional
+ * information regarding copyright ownership.
+ */
+
+/*
+ * This is just a random selection of DNSSEC configuration options.
+ */
+
+/* cut here */
+dnssec-policy "test" {
+	dnskey-ttl 3600;
+	keys {
+		ksk key-directory P1Y 13 256;
+		zsk key-directory P30D 13;
+		csk key-directory P30D 8 2048;
+	};
+	publish-safety PT3600S;
+	retire-safety PT3600S;
+	signatures-refresh P3D;
+	signatures-validity P2W;
+	signatures-validity-dnskey P14D;
+	zone-max-ttl 86400;
+	zone-propagation-delay PT5M;
+	parent-ds-ttl 7200;
+	parent-propagation-delay PT1H;
+	parent-registration-delay P1D;
+};
+options {
+	dnssec-policy "default";
+};
+zone "example1" {
+	type master;
+	dnssec-policy "test";
+	file "example1.db";
+};
+zone "example2" {
+	type master;
+	dnssec-policy "default";
+	file "example2.db";
+};