You should be able to use

[
  {
    "id": 1,
    "priority": 1,
    "action": {
      "type": "redirect",
      "redirect": {
        "url": "https://stackoverflow.com/questions"
      }
    },
    "condition": {
      "urlFilter": "https://stackoverflow.com/|",
      "resourceTypes": ["main_frame"]
    }
  }
]

since a | dictates that no more characters may come after it.

See: chrome.declarativeNetRequest - URL filter syntax - Chrome Extension API