Add CSAF downloader

* Dense and refactor ROLIE code in aggregator a bit.
* Move  advisory file processor to csaf package.
* Fix minor typo on main readme

docs/csaf_downloader.md

@@ -0,0 +1,18 @@
+## csaf_uploader
+
+### Usage
+
+```
+Usage:
+  csaf_downloader [OPTIONS] domain...
+
+Application Options:
+  -d, --directory= Directory to store the downloaded files in
+      --insecure   Do not check TLS certificates from provider
+      --version    Display version of the binary
+  -v, --verbose    Verbose output
+  -r, --rate=      The average upper limit of https operations per second
+
+Help Options:
+  -h, --help       Show this help message
+```

docs/scripts/Readme.md

@@ -25,4 +25,5 @@ Calling example (as root):
     ./TLSClientConfigsForITest.sh
     ./setupProviderForITest.sh
     ./testAggregator.sh
+    ./testDownloader.sh
 ```

docs/scripts/testDownloader.sh

@@ -0,0 +1,25 @@
+#!/usr/bin/env bash
+
+# This file is Free Software under the MIT License
+# without warranty, see README.md and LICENSES/MIT.txt for details.
+#
+# SPDX-License-Identifier: MIT
+#
+# SPDX-FileCopyrightText: 2022 German Federal Office for Information Security (BSI) <https://www.bsi.bund.de>
+# Software-Engineering: 2022 Intevation GmbH <https://intevation.de>
+
+set -e  # to exit if a command in the script fails
+
+echo
+echo '==== run downloader'
+cd ~/csaf_distribution
+
+mkdir ~/downloaded1
+
+./bin-linux-amd64/csaf_downloader --directory ../downloaded1 \
+  --rate 4.1 --verbose --insecure localhost
+
+echo
+echo '==== this was downloaded'
+cd ~/downloaded1
+find .