[client] make /var/lib/netbird paths configurable (#3084)

- NB_STATE_DIR
- NB_UNCLEAN_SHUTDOWN_RESOLV_FILE
- NB_DNS_STATE_FILE

client/internal/dns/consts.go

@@ -0,0 +1,18 @@
+//go:build !android
+
+package dns
+
+import (
+	"github.com/netbirdio/netbird/client/configs"
+	"os"
+	"path/filepath"
+)
+
+var fileUncleanShutdownResolvConfLocation string
+
+func init() {
+	fileUncleanShutdownResolvConfLocation = os.Getenv("NB_UNCLEAN_SHUTDOWN_RESOLV_FILE")
+	if fileUncleanShutdownResolvConfLocation == "" {
+		fileUncleanShutdownResolvConfLocation = filepath.Join(configs.StateDir, "resolv.conf")
+	}
+}