Introduce merge_junit script

To improve performance of Android unit tests collection. Originated it woocommerce/woocommerce-android#12064

bin/merge_junit.sh

@@ -0,0 +1,40 @@
+#!/bin/bash
+
+# Initialize variables
+reports_dir=""
+output_file=""
+
+# Function to show usage
+usage() {
+    echo "Usage: $0 -d <reports_dir> -o <output_file>"
+    exit 1
+}
+
+# Parse command-line options
+while getopts "d:o:" opt; do
+    case $opt in
+        d) reports_dir=$OPTARG ;;
+        o) output_file=$OPTARG ;;
+        ?) usage ;;
+    esac
+done
+
+# Check if both arguments were provided
+if [ -z "$reports_dir" ] || [ -z "$output_file" ]; then
+    usage
+fi
+
+# Write XML header to the output file
+echo '<?xml version="1.0" encoding="UTF-8"?>' > "$output_file"
+echo '<testsuites>' >> "$output_file"
+
+# Merge the content of all input JUnit files in the directory.
+# (Note that in the case of Unit Tests, the JUnit XML files produced by Gradle
+# don't have a parent `<testsuites>` root tag, so there's no need to try and remove it)
+sed '/<\?xml .*\?>/d' "$reports_dir"/*.xml >> "$output_file"
+
+# Close the testsuites tag
+echo '</testsuites>' >> "$output_file"
+
+# Print the result
+echo "Merged XML reports into $output_file"