Add aggregator; improve itest workflow

* Factor JSON evaluation and  construction base URLs out of of checker.
* Move json path matching to util.
* Add csaf_aggregator (as additional command)
* Improve itest workflow to checkout the branch where it is running on.

resolve #105
resolve  #72

Co-authored-by: tschmidtb51 <65305130+tschmidtb51@users.noreply.github.com>
Co-authored-by: Bernhard Reiter <bernhard@intevation.de>
Co-authored-by: Fadi Abbud <fadi.abbud@intevation.de>

util/url.go

@@ -0,0 +1,34 @@
+// 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>
+
+package util
+
+import (
+	"net/url"
+	"strings"
+)
+
+// BaseURL returns the base URL for a given URL p.
+func BaseURL(p string) (string, error) {
+	u, err := url.Parse(p)
+	if err != nil {
+		return "", err
+	}
+	ep := u.EscapedPath()
+	if idx := strings.LastIndexByte(ep, '/'); idx != -1 {
+		ep = ep[:idx+1]
+	}
+	user := u.User.String()
+	if user != "" {
+		user += "@"
+	}
+	if !strings.HasPrefix(ep, "/") {
+		ep = "/" + ep
+	}
+	return u.Scheme + "://" + user + u.Host + ep, nil
+}