Move channel info to top

Why is this change being made?

In a discussion with the Digital Production team we found that the handbook doesn't explicitly layout the uses cases for the branded and unfiltered YouTube channels. To address this, I've updated the YouTube page in the handbook. I'm going to share this MR as a proposal in #marketing Slack

@atflowers does it make sense to look at moving portions of this page from Marketing Ops to the Digital Production in the handbook?

Author Checklist

• Provided a concise title for the MR
• Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to one of the people listed in the "Maintained by" section in on the page being edited.
  • If your manager does not have merge rights, please ask someone to merge it AFTER it has been approved by your manager in #mr-buddies.
  • If the changes relate to any part of the project other than updates to content and/or data files please make sure to ping @gl-static-site-editor in a comment for a review and merge. For example changes to .gitlab-ci.yml, JavaScript/CSS/Ruby code or the layout files. (this requirement has been removed pending identification of a new DRI for the handbook)