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-keyfetcher.1

@@ -0,0 +1,64 @@
+.TH ldns-keyfetcher 1 "4 Apr 2006"
+.SH NAME
+ldns-keyfetcher \- retrieve the DNSSEC DNSKEYs for a zone
+.SH SYNOPSIS
+.B ldns-keyfetcher
+[ 
+.IR OPTIONS
+] 
+.IR DOMAIN 
+
+.SH DESCRIPTION
+\fBldns-keyfetcher\fR is used to retrieve the DNSKEYs of a zone. 
+
+First it finds all authoritative nameservers of the zone by tracing it from
+the root down. All authoritative nameservers are then queried (using TCP)
+for the DNSKEY RRset of the zone apex. If the results are all the same,
+the key resource record set is printed.
+
+
+.SH OPTIONS
+\fB-4\fR \fI\fR
+Only use IPv4
+
+\fB-6\fR \fI\fR
+Only use IPv6
+
+\fB-h\fR \fI\fR
+Show a help text and exit
+
+\fB-i\fR
+Insecurer mode; there will only be one query for the DNSKEYS. There will not
+be crosschecking of all authoritative nameservers.
+
+\fB-v\fR \fIverbosity\fR
+
+Set the verbosity level. The following levels are available:
+
+ 0: default, only print the DNSKEY RRset found, or an error on failure.
+ 1: Show the nameservers that are queried
+ 2: Show more info on what is checked
+ 3: Show the intermediate results (authority and dnskey rrsets)
+ 4: Print the answer packets that are returned
+
+\fB-r\fR \fIfile\fR
+
+Use file as the root hints file, should contain A records in presentation
+format. The default is /etc/named.root. You can get this file from
+http://www.internic.net/zones/named.root.
+
+\fB-s\fR \fI\fR
+Don't print the keys to stdout, but store them in files.
+
+The filenames will be of the format K<file>.+<alg>.+<keytag>.key
+
+.SH AUTHOR
+Written by Jelte Jansen for NLnet Labs.
+
+.SH REPORTING BUGS
+Report bugs to <dns-team@nlnetlabs.nl>.
+
+.SH COPYRIGHT
+Copyright (C) 2006 NLnet Labs. This is free software. There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
+PURPOSE.