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/test/30-load-pyldns.tpkg/30-load-pyldns.dsc

@@ -0,0 +1,14 @@
+BaseName: 30-load-pyldns
+Version: 1.0
+Description: Import pyldns module
+CreationDate: Mon Nov 12 14:53:29 CET 2012
+Maintainer: Willem Toorop
+Category: 
+Component:
+Depends: 
+Pre: 
+Post:
+Test: 30-load-pyldns.test
+AuxFiles: 
+Passed:
+Failure:

zonemaster-ldns/ldns/test/30-load-pyldns.tpkg/30-load-pyldns.help

@@ -0,0 +1,4 @@
+Synopsis: tpkg  -a ../../ exe 30-load-pyldns.tpkg
+-a path: path is where the source lives
+as the test is executed in it own subsdir it will
+need ../../ is you use a relative path

zonemaster-ldns/ldns/test/30-load-pyldns.tpkg/30-load-pyldns.test

@@ -0,0 +1,9 @@
+[ -f ../.tpkg.var.master ] && source ../.tpkg.var.master
+
+export PATH=$PATH:/usr/sbin:/sbin:/usr/local/bin:/usr/local/sbin:.
+
+# first arg is the build dir
+TPKG_BUILD=$1
+
+LD_LIBRARY_PATH=$TPKG_BUILD/.libs PYTHONPATH=$TPKG_BUILD/python-site python -c "import ldns"
+