Update Channel Services Page with a table of contents and partner service offerings

Why is this change being made?

We are updating the Channel Services Program Page to include more information about the services partners can offer.

Author Checklist

• [X ] Provided a concise title for the MR
• [ X] Added a description to this MR explaining the reasons for the proposed change, per say-why-not-just-what
• [ X] Assign this change to the correct DRI
  • If the DRI for the page/s being updated isn’t immediately clear, then assign it to your manager.
  • 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.