feat: Allow detaching help center widget (#12459)

## Summary
- allow help center portals to clear their associated web widget


Co-authored-by: Sivin Varghese <64252451+iamsivin@users.noreply.github.com>

app/javascript/dashboard/i18n/locale/en/helpCenter.json

@@ -741,7 +741,8 @@
         "LIVE_CHAT_WIDGET": {
           "LABEL": "Live chat widget",
           "PLACEHOLDER": "Select live chat widget",
-          "HELP_TEXT": "Select a live chat widget that will appear on your help center"
+          "HELP_TEXT": "Select a live chat widget that will appear on your help center",
+          "NONE_OPTION": "No widget"
         },
         "BRAND_COLOR": {
           "LABEL": "Brand color"