Add Experimentation Working Group

Why is this change being made?

To establish a working group to look at the current and proposed future state of experimentation at GitLab.

This merge request is in draft form as we work through the process of defining and setting up the group https://about.gitlab.com/company/team/structure/working-groups/#process.

https://wg-experimentation.about.gitlab-review.app/company/team/structure/working-groups/experimentation/index.html

Next steps include:

• Roles and Responsibilities (facilitator, exec sponsor, functional leads, members)
• Determine Business Goal (and page description)
• Determine Exit Criteria
• Confirm start and end dates
• Populate initial agenda https://drive.google.com/drive/search?q=title:%22Experimentation%20Working%20Group%22) (GitLab internal)

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][transparency]
• 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][mr-buddies-slack].
  • 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.