Search/NamespacedClass: Don't flag `API::Admin::Search`

Problem

API::Admin::Search is flagged by 👮 Search/NamespacedClass.

Proposed solution

• Allow namespace API::Admin::Search in Search/NamespacedClass
• Remove # rubocop:disable Search/NamespacedClass from the codebase

Discussion

The following discussion from !116650 (merged) should be addressed:

• @DylanGriffith started a discussion: (+1 comment)

  It seems this Rubocop was added in !115193 (merged) . I had to ignore it because I didn't think it made sense to put Search:: as the top level namespace here above API::Admin. Even for Ci things we have Api::Ci as the namespace. Here I've used Search before Zoekt so I assume I'm following the spirit of the rubocop rule. Perhaps the rule needs to be adjusted slightly or maybe I'm misunderstanding.

From !116650 (comment 1351306642):

@john-mason Do you think we need permit API::Admin::Search in https://gitlab.com/gitlab-org/gitlab/-/blob/c8e5c61b2cc2e098467633f40ca1bdcc68ffb97c/rubocop/cop/search/namespaced_class.rb#L23? 🤔