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

96% 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

@@ -254,7 +254,7 @@
     "myFiles": "Моите файлове",
     "newFile": "Нов файл",
     "newFolder": "Нова папка",
-    "preview": "Preview",
+    "preview": "Преглед",
     "settings": "Settings",
     "signup": "Signup",
     "siteSettings": "Site Settings"