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/docs/source/examples/index.rst

@@ -0,0 +1,12 @@
+Tutorials
+==============================
+
+Here you can find a set of simple applications which utilizes the ldns library in Python environment. 
+
+`Tutorials`
+
+.. toctree::
+	:maxdepth: 1
+	:glob:
+
+	example*