Add duplicated gin trigram index on notes note

What does this MR do?

Identified in another issue: #218410 (comment 565624409) We see that inserting a note can be very timely. It seems like recreating the index fixes the issue.

Proposed by @abrandl here #218410 (comment 571485758) we should create an identical index, then drop the old one. This MR is creating the duplicate index.

== 20210511051718 CreateIndexOnNotesNote: migrating ===========================
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:notes, :note, {:name=>"index_notes_on_note_gin_trigram", :using=>:gin, :opclass=>:gin_trgm_ops, :algorithm=>:concurrently})
   -> 0.0124s
-- execute("SET statement_timeout TO 0")
   -> 0.0010s
-- add_index(:notes, :note, {:name=>"index_notes_on_note_gin_trigram", :using=>:gin, :opclass=>:gin_trgm_ops, :algorithm=>:concurrently})
   -> 5.6516s
-- execute("RESET ALL")
   -> 0.0007s
-- transaction_open?()
   -> 0.0000s
-- indexes(:notes)
   -> 0.0049s
-- remove_index(:notes, {:algorithm=>:concurrently, :name=>"index_notes_on_note_trigram"})
   -> 0.0102s
== 20210511051718 CreateIndexOnNotesNote: migrated (5.6834s) ==================

➜  gitlab git:(add_duplicate_notes_note_trigram_index) ✗ bundle exec rake db:rollback STEP=2
== 20210511051718 CreateIndexOnNotesNote: reverting ===========================
-- transaction_open?()
   -> 0.0000s
-- indexes(:notes)
   -> 0.0103s
-- execute("SET statement_timeout TO 0")
   -> 0.0010s
-- remove_index(:notes, {:algorithm=>:concurrently, :name=>"index_notes_on_note_gin_trigram"})
   -> 0.0304s
-- execute("RESET ALL")
   -> 0.0010s
-- transaction_open?()
   -> 0.0000s
-- index_exists?(:notes, :note, {:name=>"index_notes_on_note_trigram", :using=>:gin, :opclass=>:gin_trgm_ops, :algorithm=>:concurrently})
   -> 0.0057s
-- add_index(:notes, :note, {:name=>"index_notes_on_note_trigram", :using=>:gin, :opclass=>:gin_trgm_ops, :algorithm=>:concurrently})
   -> 6.3945s
== 20210511051718 CreateIndexOnNotesNote: reverted (6.4456s) ==================

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