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/examples/nsd-test/test.queries

@@ -0,0 +1,77 @@
+# comment at start.
+; Test queries for ldns-testns.
+; This is a line based format config file.
+
+$ORIGIN example.com
+$TTL 3600
+
+# Below are the entries, they are tested for a match one by one.
+# enclose each in ENTRY_BEGIN and ENTRY_END.
+ENTRY_BEGIN
+# MATCH makes sure the query and answer match on:
+MATCH opcode qtype qname ; for default queries
+# or you can match on a specific value.
+; MATCH serial=1024 	; for this query also match SOA serial.
+; MATCH UDP 		; query must be by udp.
+#
+# REPLY lines give header info for the reply:
+# 	(opcode)  QUERY IQUERY STATUS NOTIFY UPDATE
+# 	(rcode)   NOERROR FORMERR SERVFAIL NXDOMAIN NOTIMPL YXDOMAIN 
+#		  YXRRSET NXRRSET NOTAUTH NOTZONE
+# 	(flags)   QR AA TC RD CD RA AD
+REPLY QR  	; this is a query reply.
+# ADJUST: runtime modifications to the reply. usually copy_id.
+ADJUST copy_id
+# add RRs to a section, QUESTION ANSWER AUTHORITY ADDITIONAL
+SECTION QUESTION
+# RRs, (an RR must be on a single line).
+@	IN	A
+SECTION ANSWER
+@	A	192.168.0.123
+@	TXT	"This record is unexpected."
+SECTION ADDITIONAL
+@	A	192.1.2.3
+ENTRY_END
+
+ENTRY_BEGIN
+MATCH TCP opcode qname
+ADJUST copy_id
+SECTION QUESTION
+axfr.example.com. IN AXFR
+SECTION ANSWER
+axfr.example.com. IN SOA a. b. 10 60 60 60 60 60
+bla.axfr.example.com. IN TXT "bla"
+EXTRA_PACKET
+ADJUST packet_sleep=4
+SECTION ANSWER
+bla.axfr.example.com. IN TXT "bla2"
+axfr.example.com. IN SOA a. b. 10 60 60 60 60 60
+ENTRY_END
+
+ENTRY_BEGIN
+MATCH TCP
+REPLY SERVFAIL
+ADJUST copy_id
+ldns.testns.example. TXT "The ldnstestns server handled your TCP request"
+ENTRY_END
+
+ENTRY_BEGIN
+MATCH opcode qtype qname
+MATCH serial=102
+ADJUST copy_id
+REPLY QR AA
+SECTION QUESTION
+example.net.	IXFR
+SECTION ANSWER
+example.net.	SOA	ns1.example.net. . 0 103 0 0 0
+ENTRY_END
+
+ENTRY_BEGIN
+	; Keep this as the last entry.
+	; matches anything and returns this packet.
+	; so you will get an answer for every query.
+REPLY SERVFAIL
+ADJUST copy_id
+ldns.testns.example. TXT "The ldnstestns server did not find a match for your query"
+ENTRY_END
+