feat(perf): contacts query performance (#7175)

* feat: use more indexable where condition

* feat: add index concurrently

* chore: update schema

* refactor: update index name

db/migrate/20230523104139_add_partial_index_for_resolved_contacts.rb

@@ -0,0 +1,8 @@
+class AddPartialIndexForResolvedContacts < ActiveRecord::Migration[7.0]
+  disable_ddl_transaction!
+
+  def change
+    add_index :contacts, [:account_id, :email, :phone_number, :identifier], where: "(email <> '' OR phone_number <> '' OR identifier <> '')",
+                                                                            name: 'index_contacts_on_nonempty_fields', algorithm: :concurrently
+  end
+end