Add kali-purple simple-cdd profile

This profile does the following:
- it enables the elastic apt repo
- it also enables the network during installation
- finally, it makes sure to exclude the very big package
  exploitdb-papers, otherwise the iso is too big (~ 6 GB)

I'm a bit surprised that we need to enable the network via a preseed
file. I thought that it would be enough to just make sure that the
installer-purple variant does NOT include the offline profile, but in
practice no, it's not enough.

simple-cdd/profiles/kali-purple.excludes

@@ -0,0 +1,3 @@
+# Exclude big packages that are Recommended by defensive tools metapackages.
+# Keep this list in sync with kali-meta/debian/control.
+exploitdb-papers

simple-cdd/profiles/kali-purple.postinst

@@ -0,0 +1,18 @@
+#!/bin/sh
+
+set -eu
+
+configure_elastic() {
+    # Install the elastic archive keyring
+    wget -q -O- https://artifacts.elastic.co/GPG-KEY-elasticsearch \
+    > /etc/apt/keyrings/elastic-keyring.asc
+
+    # Enable the repository
+    cat >/etc/apt/sources.list.d/elastic.list <<EOF
+deb [signed-by=/etc/apt/keyrings/elastic-keyring.asc] https://artifacts.elastic.co/packages/8.x/apt stable main
+EOF
+
+    apt-get update
+}
+
+configure_elastic

simple-cdd/profiles/kali-purple.preseed

@@ -0,0 +1,4 @@
+# Do use a network mirror, but do not upgrade, so that
+# only missing packages are fetched.
+d-i apt-setup/use_mirror boolean true
+d-i pkgsel/upgrade select none