Improve integration test for checker

* Modify script to call checker twice with difference options,
   including one with json and --verbose.
 * Add json result as build artifact to be uploaded.

.github/workflows/itest.yml

@@ -32,5 +32,7 @@ jobs:
         uses: actions/upload-artifact@v3
         with:
             name: checker-results
-            path: ~/checker-results.html
+            path: |
+                ~/checker-results.html
+                ~/checker-results.json
             if-no-files-found: error

docs/scripts/testChecker.sh

@@ -10,11 +10,15 @@
 
 set -e  # to exit if a command in the script fails
 
-echo ==== run checker
+echo '==== run checker (twice)'
 cd ~/csaf_distribution
 
 ./bin-linux-amd64/csaf_checker -o ../checker-results.html --insecure \
---client-cert ~/devca1/testclient1.crt --client-key \
-~/devca1/testclient1-key.pem localhost -f html
+    --insecure localhost -f html
 
 cat ../checker-results.html
+
+./bin-linux-amd64/csaf_checker -o ../checker-results.json --insecure \
+--client-cert ~/devca1/testclient1.crt \
+--client-key ~/devca1/testclient1-key.pem \
+--verbose localhost