fix: populate ldns submodule and add autotools to LDNS build stage

- Re-cloned zonemaster-ldns with --recurse-submodules so the bundled
  ldns C library source (including Changelog and configure.ac) is present
- Added autoconf, automake, libtool to Dockerfile.backend ldns-build stage
  so libtoolize + autoreconf can generate ldns/configure during make

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

zonemaster-ldns/ldns/contrib/python/examples/python3/ldns-higher.py

@@ -0,0 +1,36 @@
+#!/usr/bin/python
+import ldns
+
+resolver = ldns.ldns_resolver.new_frm_file("/etc/resolv.conf")
+
+dnn = ldns.ldns_dname("www.google.com")
+print(dnn.get_type_str(), dnn)
+
+dna = ldns.ldns_rdf.new_frm_str("74.125.43.99",ldns.LDNS_RDF_TYPE_A)
+print(dna.get_type_str(), dna)
+
+name = resolver.get_name_by_addr(dna)
+if (not name): raise Exception("Can't retrieve server name")
+for rr in name.rrs():
+    print(rr)
+
+name = resolver.get_name_by_addr("74.125.43.99")
+if (not name): raise Exception("Can't retrieve server name")
+for rr in name.rrs():
+    print(rr)
+
+addr = resolver.get_addr_by_name(dnn)
+if (not addr): raise Exception("Can't retrieve server address")
+for rr in addr.rrs():
+    print(rr)
+
+addr = resolver.get_addr_by_name("www.google.com")
+if (not addr): raise Exception("Can't retrieve server address")
+for rr in addr.rrs():
+    print(rr)
+
+hosts = ldns.ldns_rr_list.new_frm_file("/etc/hosts")
+if (not hosts): raise Exception("Can't retrieve the content of file")
+for rr in hosts.rrs():
+    print(rr)
+