Add back deleted build_release file

Motivation: this file is important to our publishing step

build_release.sh

@@ -0,0 +1,57 @@
+WORDPRESS_GIT_SRC_PATH="."
+DESTINATION_PATH="../onesignal-free-web-push-notifications/trunk/"
+RELEASE_ARCHIVE_FILENAME="onesignal-free-web-push-notifications.zip"
+
+# Prevent accidental rm -rf issues if running as root
+if (( EUID == 0 )); then
+  echo "Please do not run this script as root for removing directory safety reasons."
+  exit 1
+fi
+
+# Using exclude .* excludes dot files and dot directories like .git, .vscode
+if [[ $DESTINATION_PATH != *onesignal-free-web-push-notifications/trunk/ ]]; then
+ echo "Script was going to remove ${DESTINATION_PATH}, but quitting because destination path unexpectedly does not end in ...onesignal-free-web-push-notifications/trunk/. Exiting to prevent removing unexpected directory."
+ exit 1
+fi
+
+echo "Building Release Version of OneSignal WordPress Plugin"
+echo "──────────────────────────────────────────────────────"
+
+echo "Removing destination folder '${DESTINATION_PATH}'."
+rm -rf $DESTINATION_PATH
+
+echo "Creating new empty destination folder '${DESTINATION_PATH}'."
+mkdir -p $DESTINATION_PATH
+
+# The --delete option remove files from destination that are not present in source
+exclude_options=(
+    "--exclude=.git/"
+    "--exclude=.env"
+    "--exclude=.gitignore"
+    "--exclude=.github"
+    "--exclude=.vscode/"
+    "--exclude=build_release.sh"
+    "--exclude=*.zip"
+    "--exclude=onesignal-free-web-push-notifications"
+    "--exclude=onesignal-free-web-push-notifications.zip"
+    "--exclude=CONTRIBUTING.md"
+    "--exclude=LICENSE"
+    "--exclude=docker*"
+    "--exclude=PluginDevDockerUsage.md"
+    "--exclude=README.md"
+    "--exclude=index.php"
+    "--exclude=views/css/*.scss"
+    "--exclude=views/css/callout.css"
+    "--exclude=views/css/link.css"
+    "--exclude=views/css/link.css"
+    "--exclude=views/css/semantic-ui"
+)
+rsync --archive --delete "${exclude_options[@]}" $WORDPRESS_GIT_SRC_PATH/ $DESTINATION_PATH
+
+# Add new unversioned directories to SVN
+svn status $DESTINATION_PATH | grep "^\?" | awk '{print $2}' | xargs -I {} svn add {}
+
+echo "Creating archive of release contents as '${RELEASE_ARCHIVE_FILENAME}' in source directory '${WORDPRESS_GIT_SRC_PATH}'."
+cd $WORDPRESS_GIT_SRC_PATH
+zip -qr -x ".*" -x="build_release.sh" -x="*.zip" -x="onesignal-free-web-push-notifications" ${RELEASE_ARCHIVE_FILENAME} ./*
+cd -