Add auxiliary files needed for AppImage

AppRun is the file that gets packaged inside of the AppImage that bootstraps the application.
The AppImage can only have one icon, so we use the largest sample we have available.
The appdata.xml contains some metadata.

Contributes to issue CURA-9409.

packaging/AppRun

@@ -0,0 +1,16 @@
+#!/bin/sh
+
+scriptdir=$(dirname $0)
+
+export PYTHONPATH="$scriptdir/lib/python3.10"
+export LD_LIBRARY_PATH=$scriptdir
+export QT_PLUGIN_PATH="$scriptdir/qt/plugins"
+export QML2_IMPORT_PATH="$scriptdir/qt/qml"
+export QT_QPA_FONTDIR=/usr/share/fonts
+export QT_QPA_PLATFORMTHEME=xdgdesktopportal
+export QT_XKB_CONFIG_ROOT=/usr/share/X11/xkb
+
+# Use the openssl.cnf packaged in the AppImage
+export OPENSSL_CONF="$scriptdir/openssl.cnf"
+
+$scriptdir/Ultimaker-Cura "$@"

packaging/cura.appdata.xml

@@ -0,0 +1,18 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<component type="desktop-application">
+	<id>com.ultimaker.cura</id>
+	<metadata_license>CC0-1.0</metadata_license>
+	<project_license>LGPL-3.0</project_license>
+	<name>Ultimaker Cura</name>
+	<summary>Slicer to prepare your 3D printing projects</summary>
+	<description>
+		<p>Ultimaker Cura is a slicer, an application that prepares your model for 3D printing. Optimized, expert-tested profiles for 3D printers and materials mean you can start printing reliably in no time. And with industry-standard software integration, you can streamline your workflow for maximum efficiency.</p>
+	</description>
+	<url type="homepage">https://ultimaker.com/en/software/ultimaker-cura</url>
+	<screenshots>
+		<screenshot type="default">
+			<caption>Print preparation screen</caption>
+			<image>https://raw.githubusercontent.com/Ultimaker/Cura/master/screenshot.png</image>
+		</screenshot>
+	</screenshots>
+</component>