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-nsec3-hash.1

@@ -0,0 +1,34 @@
+.TH ldns-nsec3-hash.c 1 "10 Dec 2008"
+.SH NAME
+ldns-nsec3-hash \- print out the NSEC3 hash for a domain name
+.SH SYNOPSIS
+.B ldns-nsec3-hash
+.IR <domain_name>
+
+.SH DESCRIPTION
+\fBldns-nsec3-hash\fR is used to print out the NSEC3 hash for the given domain name.
+
+.SH OPTIONS
+.TP
+\fB-a\fR \fInumber\fR
+Use the given algorithm number for the hash calculation. Defaults to 1 (SHA-1).
+
+.TP
+\fB-s\fR \fIsalt\fR
+Use the given salt for the hash calculation. Salt value should be in hexadecimal format.
+
+.TP
+\fB-t\fR \fIcount\fR
+Use count iterations for the hash calculation.
+
+
+.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) 2008 NLnet Labs. This is free software. There is NO
+warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR
+PURPOSE.