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

88% 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

@@ -235,7 +235,7 @@
       "light": "Светла",
       "title": "Тема"
     },
-    "user": "User",
+    "user": "Потребител",
     "userCommands": "Commands",
     "userCommandsHelp": "A space separated list with the available commands for this user. Example:\n",
     "userCreated": "User created!",