Update Consortium Membership Section of the OSS Handbook Page

Why is this change being made?

This merge request makes the following changes to the Consortium Membership section of the GitLab for Open Source handbook page:

• Adds more details to the consortium membership detail area, including who our current board seats are
• Removes the CDF membership since we're in the process of cancelling
• Adds a link to the issue associated with each membership. Since these issues create sensitive information like cost of membership and contact details, these issues are confidential and accessible to the GitLab team only
• Adds information about elections and documents how we've participated so far

This merge request closes issue: https://gitlab.com/gitlab-com/marketing/community-relations/opensource-program/consortium-memberships/-/issues/15

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)