Disable MissingFeatureCategory for JH

What does this MR do and why?

Disable Rubocop rule RSpec/MissingFeatureCategory for JH.

Feature Categorization Reference doc: https://docs.gitlab.com/ee/development/feature_categorization

This is done for error budgeting, alert routing, and team attribution.

JH team is not defined in the stages.yml file, so there is no suitable feature_category value.

https://gitlab.com/gitlab-com/www-gitlab-com/blob/master/data/stages.yml

And, we can accurately find the responsible colleagues through Git blame, so feature_category is not necessary.

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/cc EM @mtan-gitlab-cn