Change all the cache docs to use new configurable URL from 1.0

[rmloveland]

For details, see relevant sections of this docs PR and this JS one.

[rmloveland]

In this case we will consider "all the cache docs" to be just Show Video Ads, which is addressed by PR #496

There is additional work needed to update the Prebid.org-hosted video example pages, which has been captured in #508