feat(dns): replace unbound with qdm12/dns@v2.0.0-beta-rc6 (#1742)

- Faster start up
- Clearer error messages
- Allow for more Gluetun-specific customization
- DNSSEC validation is dropped for now (it's sort of unneeded)
- Fix #137

internal/configuration/settings/deprecated.go

@@ -0,0 +1,25 @@
+package settings
+
+import (
+	"slices"
+
+	"github.com/qdm12/gosettings/reader"
+	"golang.org/x/exp/maps"
+)
+
+func readObsolete(r *reader.Reader) (warnings []string) {
+	keyToMessage := map[string]string{
+		"DOT_VERBOSITY":           "DOT_VERBOSITY is obsolete, use LOG_LEVEL instead.",
+		"DOT_VERBOSITY_DETAILS":   "DOT_VERBOSITY_DETAILS is obsolete because it was specific to Unbound.",
+		"DOT_VALIDATION_LOGLEVEL": "DOT_VALIDATION_LOGLEVEL is obsolete because DNSSEC validation is not implemented.",
+	}
+	sortedKeys := maps.Keys(keyToMessage)
+	slices.Sort(sortedKeys)
+	warnings = make([]string, 0, len(keyToMessage))
+	for _, key := range sortedKeys {
+		if r.Get(key) != nil {
+			warnings = append(warnings, keyToMessage[key])
+		}
+	}
+	return warnings
+}