Allowed "view site" request to save cookies in cross-origin requests

no issue

- adds `credentials: 'include'` option to `fetch()` which instructs browsers to save cookies in the POST response in cross-origin requests (default is `'same-origin'`)

ghost/admin/app/routes/site.js

@@ -21,6 +21,7 @@ export default AuthenticatedRoute.extend({
                 method: 'POST',
                 mode: 'cors',
                 redirect: 'manual',
+                credentials: 'include',
                 headers: {
                     'Content-Type': 'application/x-www-form-urlencoded'
                 },