Add v2 to reserved top level routes [EE]

Dmytro Zaporozhets (DZ)requested to merge
dz-reserve-v2-root-path-ee into master

What does this MR do?

Adds v2 to top level reserved routes

What are the relevant issue numbers?

EE version of https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/26540

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