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/DNS-LDNS/t/testdata/key.private

@@ -0,0 +1,13 @@
+Private-key-format: v1.2
+Algorithm: 7 (NSEC3RSASHA1)
+Modulus: +D+CE6ST+vFtbnXLdNESSprWSpbpRqEyri20vOx/JIViYdflGQyT0SDWSAE0JqtRlq73qSTDNuR3KWG/57oQQQ5P/wdQaF4TXA/nGjQJPEnhwKVUPVl5WRvqJLpW3C5xSSkhUkwjCp8y6z4NkbX0x7kum9ZTyTai6hkAhjyXu56yXAHX80DWadGK7RmX4JNlJalp2O33hJmakw8BVpgM9yaN4TixVsmZyHLi4hLjMAsjkEEJnfV8WoMEyyjs4kdKDHQAIa854loRcOluT1FiBKgecVAjDu/mkxnqYedN68Yx/wi7D+eClGf/gZjsmuoKKxCxnvDkRCKxrdMJtrsduw==
+PublicExponent: AQAB
+PrivateExponent: A8m0SmhweZvFd7IEcLvf85N5QZob5SAAjffUki1poz0Fy0hoDoHKn55IpsCd8xkaHZp93O7aq7PAvbjoHLkSFmwJfHK4H1+QHA+CDzxMB8d40l+zcVw0Jc/vOrA9Mw7iW6NtBrxyrG7RcBV6T4bfPUzuESKsFJ3oznmjMGksR4iUrnYAoUgi1pCQlxhSkPM74YhNWbUxYr4gRlL2xGGcJ2qMM8KG06or/Ok+d4bxnxiDBo41THik8ptfu/DL3HrJLOJ1CrvZGy9Q3uFiCvfD9Sk+eOZz1XPkJrUDKGYGoUvZc8enStXSM+TKd3EQy5owjJt+j2h0JdYJM8pxF2EWwQ==
+Prime1: /5r4e+6kJS/+UJ0DMenJGm0vxfgFHvk5yLfz+1sKd6C9qQJN5da1m6kWuPdtBG7XGhZb8cJPOfK//g9hVS9GYEDyYmhYZsPTL+1vkiecDpeEQkrf4RCtU7NXLNT/AVNe01iEnIGuKbva6z19P1hjNO23d7LXHil1oULM1W8O1Z8=
+Prime2: +KGhJOe+dB5Ud9cFlspMIIpZKHvoDc8VUb2avnhicDX5YC8dVS3nBoyc1cBNgxi4nSvBSl8/fwNT1cHJsPj7Xp2FOAsIBITRnmQt2P5JDpTEuMkEjMT8h/gJ8WnJ0+/VQhLG6rfsSAXdXvVhP4VYttPdiQ0fAe8b5v2MH1VzamU=
+Exponent1: UWCEVeifR9ukywOCHeUBirFScWPKNZdBR18RhWfxyC5b07ARHuihvyIxQsg7ZBrpzrtpoGmtkZRwfbFl2poHfOOQh7YS1vzngq3ERLLpo1en2vc9mckWdbx2N6bEXSau3Pikl7NNwKm3RAe6lW1NgG9iZvCAPnESqzm6PwVxop8=
+Exponent2: FMsnt/dttTZoKBGilQbcMQiBBmK+eJEuHkT2MSHOUcYh0gp+sIYDQUf3QeUwVlt17ScgpkCrBctYcpMfdB6On04bOyGpDP+yrEWClBhIMeD9RtsA92juGc0Dv93yFDiFpF3/pte0+h0Lc4qgFHjpf3jemTywsC+4LKxd0K0L1wU=
+Coefficient: klnXksRr0Z8HPLASytPt4EeBK3Md7MM+Ihm6DIM5PA/KO9k0s8231hspcxBDj37HYwJ7eD77svUJFzdUOqIT8gChc6uq9VI9NFggs8rn4EndoEe+zU477NpL4U09LMfbAN+NATkhDWabVIQBeGqpIAR0fxFIqGhDtkiLyNqhq3c=
+Created: 20120614100023
+Publish: 20120614100023
+Activate: 20120614100023

zonemaster-ldns/ldns/contrib/DNS-LDNS/t/testdata/myzone.org

@@ -0,0 +1,17 @@
+$TTL 4500
+$ORIGIN myzone.org.
+
+myzone.org. 1000 IN SOA (
+	    ldns.myzone.org. 
+	    ns.ldns.myzone.org. 
+	    2012113030 		   
+	    12345 
+	    1827 
+	    2345678 
+	    87654 )
+
+ns.ldns     A 192.168.100.2
+ns2 5600 IN AAAA 2001:dead:dead::2
+ns2 6600 IN A 192.168.100.7
+ns1 3600 IN A 192.168.100.2
+ns1 4600 IN AAAA 2001:dead:dead::1

zonemaster-ldns/ldns/contrib/DNS-LDNS/t/testdata/resolv.conf

@@ -0,0 +1,3 @@
+nameserver 127.0.0.1
+nameserver 192.168.100.1
+search foo.bar.org