Migrate mentions for design notes

Number of rows affected

Design notes with mentions ~652

  explain select id from notes where noteable_type = ‘DesignManagement::Design’ and note like ‘%\@%’

Index Scan using index_notes_on_noteable_id_and_noteable_type on public.notes  (cost=0.57..4519075.97 rows=3936 width=4) (actual time=7.361..952352.359 rows=652 loops=1)
   Index Cond: ((notes.noteable_type)::text = 'DesignManagement::Design'::text)
   Filter: (notes.note ~~ '%\@%'::text)
   Rows Removed by Filter: 1535
   Buffers: shared hit=107 read=1362816 dirtied=17
   I/O Timings: read=938952.612