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>

cmd/csaf_checker/util.go

@@ -1,49 +0,0 @@
-// 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: 2021 German Federal Office for Information Security (BSI) <https://www.bsi.bund.de>
-// Software-Engineering: 2021 Intevation GmbH <https://intevation.de>
-
-package main
-
-import (
-	"bufio"
-	"encoding/hex"
-	"io"
-	"net/url"
-	"regexp"
-	"strings"
-)
-
-var hexRe = regexp.MustCompile(`^([[:xdigit:]]+)`)
-
-func hashFromReader(r io.Reader) ([]byte, error) {
-	scanner := bufio.NewScanner(r)
-	for scanner.Scan() {
-		if m := hexRe.FindStringSubmatch(scanner.Text()); m != nil {
-			return hex.DecodeString(m[1])
-		}
-	}
-	return nil, scanner.Err()
-}
-
-func basePath(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
-}