chore: Display Agent Bot token after creation (#11488)

This PR includes:

- Displaying the Agent Bot token after creation
- Updating the avatar icon when an avatar image is not present

Fixes: https://linear.app/chatwoot/issue/CW-4337/agent-bot-token-not-visible

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

@@ -59,6 +59,11 @@
         "ERROR_MESSAGE": "Could not update bot. Please try again."
       }
     },
+    "ACCESS_TOKEN": {
+      "TITLE": "Access Token",
+      "DESCRIPTION": "Copy the access token and save it securely",
+      "COPY_SUCCESSFUL": "Access token copied to clipboard"
+    },
     "FORM": {
       "AVATAR": {
         "LABEL": "Bot avatar"