Change UKVI cohort test copy and frequency

Now that we've gathered sufficient data, we're changing the bucket to be 50/50. Along with this we're changing the copy to test whether users will be able to find the answers they want directly on GOV.UK instead of phoning the call centres directly.

Please see me for any other history or context if required.

As part of this we need to change the bucket key so the experiment begins with fresh cohorts.