feat: added functionality to measure size of volume

README.MD

@@ -45,3 +45,10 @@
    ```bash
    docker run --rm -v <persistent-volume-name>:/data -v /path/to/backup:/app ghcr.io/swiftwave-org/volume-toolkit import
    ```
+3. Measure the size of a persistent volume
+
+   a. Run the following command
+   ```bash
+   docker run --rm -v <persistent-volume-name>:/data  -v /path/to/backup:/app volume-toolkit size
+   ```
+   b. The size of the persistent volume will be written in `/path/to/backup/size.txt` file in bytes format.

volume_toolkit

@@ -11,7 +11,11 @@ elif [ "$1" == "import" ]; then
         echo "dump.tar.gz not found"
         exit 1
     fi
+elif [ "$1" == "size" ]; then
+    size=$(du -sb /data | awk '{print $1}')
+    printf "%s" "$size" > /app/size.txt
+    exit 0
 else
-    echo "Usage: volume_export.sh [export|import]"
+    echo "Usage: [export|import|size]"
     exit 1
 fi