Newsletter subscriptions page creates broken URL when left open for a period of time

[robhudson]

Description

With the page open over a lunch break, then editing the form and submitting, I see 2 requests in my network panel...

1. OPTIONS https://<basket-url>/news/user//
2. POST https://<basket-url>/news/user//

Looks like the token expired since I opened the page and when I submitted the form.

Steps to reproduce

1. Open https://www.mozilla.org/en-US/newsletter/existing/<token>/
2. Wait about an hour
3. Submit the form

[alexgibson]

Yeah, looks like the cookie we set lasts for 1 hour. I'm not sure if we need to extend the duration (?), but we should probably fail more gracefully and redirect back to /recovery/ when it expires.