Add a GovStore fallback rule to redirect /* to its GOV.UK start page

- If and only if the path does not match any of the previous regexen -
  see
  https://github.com/alphagov/bouncer/commit/c29b447b63389d0b2d7f230565ae1b847481f01d.
- This encompasses /cloudstore/supplier, so delete that rule.
This description sounds a bit misleading because some paths starting with `/cloudstore` will fallback to the rule this is testing. Perhaps `'visiting a GovStore URL that isn\'t for a supplier in a category'` instead, to express the intent more clearly?

Maybe the intent would be clearer if this test were also at the bottom, so that the tests are in the same order as the rules they're testing.