Pull request 2111: 6545-schema-version

Updates #6545.

Squashed commit of the following:

commit b1969128a99ff21c97feb4e7805b4b8133d7122f
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Dec 15 20:04:37 2023 +0300

    home: fix import

commit 872ccea1491a8da76cc24db79247438d0ce4d256
Author: Ainar Garipov <A.Garipov@AdGuard.COM>
Date:   Fri Dec 15 20:01:15 2023 +0300

    all: output schema version

internal/configmigrate/v3.go

@@ -0,0 +1,31 @@
+package configmigrate
+
+// migrateTo3 performs the following changes:
+//
+//	# BEFORE:
+//	'schema_version': 2
+//	'dns':
+//	  'bootstrap_dns': '1.1.1.1'
+//	  # …
+//
+//	# AFTER:
+//	'schema_version': 3
+//	'dns':
+//	  'bootstrap_dns':
+//	  - '1.1.1.1'
+//	  # …
+func migrateTo3(diskConf yobj) (err error) {
+	diskConf["schema_version"] = 3
+
+	dnsConfig, ok, err := fieldVal[yobj](diskConf, "dns")
+	if !ok {
+		return err
+	}
+
+	bootstrapDNS, ok, err := fieldVal[any](dnsConfig, "bootstrap_dns")
+	if ok {
+		dnsConfig["bootstrap_dns"] = yarr{bootstrapDNS}
+	}
+
+	return err
+}