Add Enrique Alcantara expertise

Why is this change being made?

It establishes Enrique Alcántara as a Frontend expert for the Static Site Editor product and GitLab UI. It helps contributors to have a point of contact in those domain areas.

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