PLT-6706: add /code command (#6936)

* add /code command

* return an error for empty /code message

i18n/en.json

@@ -919,6 +919,22 @@
     "id": "api.command_shortcuts.nav.unread_prev",
     "translation": "ALT+SHIFT+UP: Previous channel or direct message in left hand sidebar with unread messages\n"
   },
+  {
+    "id": "api.command_code.desc",
+    "translation": "Display text as a code block"
+  },
+  {
+    "id": "api.command_code.hint",
+    "translation": "[text]"
+  },
+  {
+    "id": "api.command_code.name",
+    "translation": "code"
+  },
+  {
+    "id": "api.command_code.message.app_error",
+    "translation": "A message must be provided with the /code command."
+  },
   {
     "id": "api.command_shrug.desc",
     "translation": "Adds ¯\\_(ツ)_/¯ to your message"