Add CEO Shadows to alumni list

Why is this change being made?

Adding @brittanyr, @Vatalidis, @dstanley, @chloe, and @sarahwaldner to the CEO Shadow alumni.

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Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what