Closes: https://github.com/fleetdm/fleet/issues/18448
Changes:
- Updated `create-vanta-authorization-request` to return an
`invalidResponseFromFleetInstance ` response when a response from a
Fleet instance does not contain the expected values (A `user` object for
a request to the `/me` endpoint and a `license` object for the request
to the `/config` endpoint.)
- Updated the /connect-vanta page to show an error message to users
asking them to verify the URL of their Fleet instance if the API
response is invalid.