Move redirect setup policy to the handbook-usage page
During a conversation on Slack, it became clear that we needed a policy in the handbook for setting up redirects when pages are moved or page names are altered. Fortunately, the Marketing team already had a policy in their section of the handbook that @sytses suggested should be moved to the /handbook-usage/ page.
This MR migrates that content, provides a link to the new content location in the original Marketing page, and updates the policy slightly with @northrup's instructions for opening issues in the Infrastructure channel rather than requesting redirects exclusively through Slack.
This change does not yet incorporate @williamchia's suggestions in this issue