Change the URL JSDOM uses for the current page
Change the URL JSDOM uses for the current page

https://jestjs.io/docs/en/configuration#testurl-string

Affects all DOM APIs that return information about
the URL, for example window.location.

Why:

We now have tests for setting/deleting cookies.
Tough-cookie, the library JSDOM uses for cookie
handling cookies doesn't allow setting cookies
with `domain=localhost`. This is correct by
RFC6265, the standard it follows, as domains must
have 2 or more `.`s in them.

The only way to set a cookie on `localhost` is to
leave out the `domain` attribute.

The code we are testing sets and deletes cookies
set on specific domains so using `localhost` is
out.

We also cannot just set/delete cookies on the
domains used as cookies are required to match the
domain of the current page.

The solution we are left with is to set the
current page to one from production and make sure
each cookie is set relative to that domain.

Note: this introduces `testURL` in isolation to be
sure it doesn't break any existing tests.

alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin,alphagov/notifications-admin