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

@@ -255,8 +255,8 @@
     "newFile": "Нов файл",
     "newFolder": "Нова папка",
     "preview": "Преглед",
-    "settings": "Settings",
-    "signup": "Signup",
+    "settings": "Настройки",
+    "signup": "Абониране",
     "siteSettings": "Site Settings"
   },
   "success": {