feat(i18n): add detailed compression level descriptions to en-GB locale

- Added new i18n keys for compression level descriptions in `translation.json`
- Defined ranges of compression levels with explanations about quality and file size
- Ensured consistency and readability for the updated descriptions

Signed-off-by: Balázs Szücs <bszucs1209@gmail.com>

frontend/public/locales/en-GB/translation.json

@@ -3338,6 +3338,11 @@
         "bullet1": "Lower values preserve quality",
         "bullet2": "Higher values reduce file size"
       },
+      "compressionLevel": {
+        "range1to3": "Lower values preserve quality but result in larger files",
+        "range4to6": "Medium compression with moderate quality reduction",
+        "range7to9": "Higher values reduce file size significantly but may reduce image clarity"
+      },
       "grayscale": {
         "title": "Grayscale",
         "text": "Select this option to convert all images to black and white, which can significantly reduce file size especially for scanned PDFs or image-heavy documents."
@@ -3355,6 +3360,11 @@
       "4": "Auto mode - Auto adjusts quality to get PDF to exact size",
       "5": "Expected PDF Size (e.g. 25MB, 10.8MB, 25KB)"
     },
+    "compressionLevel": {
+      "range1to3": "Lower values preserve quality but result in larger files",
+      "range4to6": "Medium compression with moderate quality reduction",
+      "range7to9": "Higher values reduce file size significantly but may reduce image clarity"
+    },
     "submit": "Compress"
   },
   "decrypt": {