Add Testing team feature flag table

Why is this change being made?

There currently is not a SSOT of feature flags that belong to grouptesting. This table will temporarily be the SSOT until issues can be made to track them and we can replace the table with an issue filter link. This is step 1 in a 3 step process to keep track of our feature flags more efficiently.

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 change relates to any part of the project other than updates to content and/or data files (e.g. team.yml) please make sure to ping @gl-static-site-editor in a comment for a review and merge.
  • If the DRI for the page/s being updated isn't immediate 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

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