AO3 6846 Add admin_hidden_work_notification mailer #5016

Job	Run time
rake db:otwseed	1m 17s
rspec spec/controllers	13m 58s
rspec spec/models	5m 32s
rspec --exclude-pattern 'spec/{controllers,models}/*/.rb'	9m 2s
cucumber features/admins	6m 50s
cucumber features/bookmarks	4m 53s
cucumber features/collections	7m 3s
cucumber features/comments_and_kudos	6m 51s
cucumber features/gift_exchanges	8m 18s
cucumber features/importing	2m 42s
cucumber features/other_a	11m 28s
cucumber features/other_b	7m 9s
cucumber features/prompt_memes_a	3m 52s
cucumber features/prompt_memes_b	3m 42s
cucumber features/prompt_memes_c	4m 52s
cucumber features/search	6m 32s
cucumber features/tag_sets	3m 26s
cucumber features/tags_and_wrangling	6m 40s
cucumber features/users	5m 58s
cucumber features/works	13m 55s
	2h 14m 0s

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