feat: Translate frontend/src/i18n/en.json in bg

54% of minimum 50% translated source file: 'frontend/src/i18n/en.json'
on 'bg'.

Sync of partially translated files: 
untranslated content is included with an empty translation 
or source language content depending on file format

frontend/src/i18n/bg.json

@@ -148,8 +148,8 @@
     "discardEditorChanges": "Сигурни ли сте, че искате да откажете направените промени?"
   },
   "search": {
-    "images": "Images",
-    "music": "Music",
+    "images": "Изображения",
+    "music": "Музика",
     "pdf": "PDF",
     "pressToSearch": "Press enter to search...",
     "search": "Search...",