Bridge zombienet tests - move all test scripts to the same folder (#3333)

Related to https://github.com/paritytech/polkadot-sdk/issues/3242

bridges/testing/scripts/sync-exit.sh

@@ -0,0 +1,14 @@
+#!/bin/bash
+set -e
+
+# every network adds a char to the file, let's remove ours
+truncate -s -1 $TEST_FOLDER/exit-sync
+
+# when all chars are removed, then our test is done
+while true
+do
+    if [ `stat --printf="%s" $TEST_FOLDER/exit-sync` -eq 0 ]; then
+        exit
+    fi
+    sleep 100
+done