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-revoke.1

@@ -0,0 +1,27 @@
+.TH ldns-revoke 1 "23 Jul 2008"
+.SH NAME
+ldns-revoke \- sets the revoke bit of a DNSKEY
+.SH SYNOPSIS
+.B ldns-revoke
+.IR file
+
+.SH DESCRIPTION
+\fBldns-revoke\fR is used to revoke a public DNSKEY RR.
+When run it will read \fIfile\fR with a DNSKEY RR in it, 
+sets the revoke bit and write back the output to \fIfile\fR .
+
+.SH OPTIONS
+.TP
+\fB-n\fR
+Write the result to stdout instead of a file
+
+.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.