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/hash.go

@@ -0,0 +1,66 @@
+// 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 (
+	"bufio"
+	"encoding/hex"
+	"fmt"
+	"hash"
+	"io"
+	"os"
+	"regexp"
+)
+
+var hexRe = regexp.MustCompile(`^([[:xdigit:]]+)`)
+
+// HashFromReader reads a base 16 coded hash sum from a reader.
+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()
+}
+
+// HashFromFile reads a base 16 coded hash sum from a file.
+func HashFromFile(fname string) ([]byte, error) {
+	f, err := os.Open(fname)
+	if err != nil {
+		return nil, err
+	}
+	defer f.Close()
+	return HashFromReader(f)
+}
+
+// WriteHashToFile writes a hash of data to file fname.
+func WriteHashToFile(fname, name string, h hash.Hash, data []byte) error {
+	if _, err := h.Write(data); err != nil {
+		return err
+	}
+
+	f, err := os.Create(fname)
+	if err != nil {
+		return err
+	}
+	fmt.Fprintf(f, "%x %s\n", h.Sum(nil), name)
+	return f.Close()
+}
+
+// WriteHashSumToFile writes a hash sum to file fname.
+func WriteHashSumToFile(fname, name string, sum []byte) error {
+	f, err := os.Create(fname)
+	if err != nil {
+		return err
+	}
+	fmt.Fprintf(f, "%x %s\n", sum, name)
+	return f.Close()
+}