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/ldns-test-edns.1

@@ -0,0 +1,41 @@
+.TH ldns-test-edns 1 "14 Dec 2010"
+.SH NAME
+ldns-test-edns \- test if dns cache supports EDNS and DNSSEC.
+.SH SYNOPSIS
+.B ldns-test-edns
+[
+.IR -i
+]
+{
+.IR ip 
+}
+.SH DESCRIPTION
+\fBldns-test-edns\fR tests a DNS cache and checks if it supports EDNS0 and
+DNSSEC types so that it can be used as a dnssec-enabled DNS cache.  It sends
+two queries to the cache, one for the root key and one for a DS record.
+These must succeed, the answer must have EDNS, that type and signatures.
+.PP
+If the IP address is good for DNSSEC, it is printed with 'OK'.  Otherwise
+short description is given of the failure.
+If OK is given, the cache should be good to use as a cache for a local
+configured DNSSEC validator.
+.PP
+The tool assumes the root is signed and Sweden is signed.
+Also, the queries are sent with the CD flag, the tool does not check that the
+results are validated, but that they \fBcan\fR be validated.
+.SH OPTIONS
+\fB-i\fR option enables a mode where the working IP addresses are printed
+after another, with no other explanations, and if none work or no IP addresses
+are on the input, 'off' is printed.
+.PP
+\fBldns-test-edns\fR takes one or more IP addresses, it checks them in turn.
+IPv4 and IPv6 addresses can be given.  The exit value is for the last checked
+IP address: 0 is OK, 1 is failure, 2 is some sort of network failure.
+.SH AUTHOR
+Written by the ldns team as an example for ldns usage.
+.SH REPORTING BUGS
+Report bugs to <dns-team@nlnetlabs.nl>.
+.SH COPYRIGHT
+Copyright (C) 2010 NLnet Labs. This is free software. There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
+PURPOSE.