Add metadata in rspec files ee/controllers/admin

What does this MR do and why?

Describe in detail what your merge request does and why.

Related #381801 (closed)

This MR updates feature_category for RSpec files for

• https://gitlab.com/gitlab-org/gitlab/-/tree/master/ee/spec/controllers/admin
• https://gitlab.com/gitlab-org/gitlab/-/tree/master/ee/spec/controllers/concerns

This information is added to flaky tests reports and from here we can automatically quarantine tests and create issues for the related feature and group owning the feature.

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