Fix performance analytics rubocop

What does this MR do and why?

Fix performance analytics rubocop

jh/lib/gitlab/analytics/performance_analytics/group_report.rb:33:25: C: [Correctable] Rails/IndexWith: Prefer index_with over to_h { ... }.
          column_data = COLUMN_KEYS.to_h do |key| ...
                        ^^^^^^^^^^^^^^^^^^^^^^^^^
jh/lib/gitlab/analytics/performance_analytics/group_report.rb:57:25: C: [Correctable] Rails/IndexWith: Prefer index_with over to_h { ... }.
          column_data = COLUMN_KEYS.to_h do |key| ...
                        ^^^^^^^^^^^^^^^^^^^^^^^^^
jh/lib/gitlab/analytics/performance_analytics/group_report.rb:82:44: C: [Correctable] Rails/IndexWith: Prefer index_with over to_h { ... }.
            { "username" => "Name" }.merge(COLUMN_KEYS.to_h { |key| [key, column_class(key).header] })
                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
jh/lib/gitlab/analytics/performance_analytics/project_report.rb:76:26: C: [Correctable] Rails/IndexWith: Prefer index_with over to_h { ... }.
            query_data = COLUMN_KEYS.to_h do |key| ...
                         ^^^^^^^^^^^^^^^^^^^^^^^^^
jh/lib/gitlab/analytics/performance_analytics/project_report.rb:94:44: C: [Correctable] Rails/IndexWith: Prefer index_with over to_h { ... }.
            { "username" => "Name" }.merge(COLUMN_KEYS.to_h { |key| [key, column_class(key).header] })
                                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

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