Update video examples to not rely on a bidder being available and willing to bid

[dgirardi]

Sometimes the appnexus adapter will not bid - which is not great for example pages.

Originally posted by @dgirardi in #11247

Instead of using real bidders and test accounts, this could be done with the debugging module. To avoid generating confusion with debugging config in the example html, we could have "token" bidders set up in a separate js file; something like:

// docs.prebid.org/files/example-setup.js

pbjs.que.push(() => {
   pbjs.setConfig({
      debugging: {
          enabled: true,
          intercept: [{
              when: {
                    bidder: 'outstreamBidder',
              },
              then: {
                    vastXml: '...'
              }
          }]
      }
   })
})

then link to it and use token bidders from examples:

// ...
<script aysnc src="jsdelivr/prebid.js">
<script async src="docs.prebid.org/files/example-stetup.js">
<script>
   pbjs.addAdUnits([{
        //...
        bids: [{
         bidder: 'outstreamBidder'
        }]
   }])
</script>

[patmmccann]

prebid/Prebid.js#10944 (comment) has a suggestion on changing the example structure