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-update.1

@@ -0,0 +1,52 @@
+.TH ldns-update 1 "30 May 2005"
+.SH NAME
+ldns-update \- send a dynamic update packet
+.SH SYNOPSIS
+.B ldns-update
+.IR name
+[
+.IR zone
+]
+[
+.IR ip
+]
+[
+.IR tsig_name
+.IR tsig_alg
+.IR tsig_hmac
+] 
+
+.SH DESCRIPTION
+\fBldns-update\fR is used to send a dynamic update packet.
+
+.SH OPTIONS
+.TP
+\fBname\fR
+The domainname to associate with the given \fBip\fR address.
+
+.TP
+\fBzone\fR
+When given uses this \fBzone\fR instead of trying to find and process \fBdomain\fR's SOA record.
+
+.TP
+\fBip\fR
+Send the update to this IP address.
+Or, when the literal text \fBnone\fR is given, remove any previous addresses.
+
+.TP
+\fBtsig_name tsig_alg tsig_hmac\fR
+Use TSIG (rfc2845) to authenticate.
+
+.SH EXAMPLE
+ldns-update my.example.org 1.2.3.4
+
+.SH AUTHOR
+Written by Jakob Schlyter and Håkan Olsson, as an addition to the ldns library from NLnet Labs.
+
+.SH REPORTING BUGS
+Report bugs to <dns-team@nlnetlabs.nl>.
+
+.SH COPYRIGHT
+Copyright (C) 2005 NLnet Labs. This is free software. There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
+PURPOSE.