LG-1384 Fix phone configuration index (#2989)

**Why**: To prevent full table scans and db outages

**How**: Add new index prefixed with user_id to phone_configurations.  Drop old index.

db/migrate/20190604110233_fix_phone_configuration_index.rb

@@ -0,0 +1,22 @@
+class FixPhoneConfigurationIndex < ActiveRecord::Migration[5.1]
+  disable_ddl_transaction!
+
+  def up
+    add_index(
+      :phone_configurations,
+      %i[user_id made_default_at created_at],
+      algorithm: :concurrently,
+      name: 'index_phone_configurations_on_made_default_at',
+    )
+    remove_index :phone_configurations, %i[made_default_at created_at]
+  end
+
+  def down
+    remove_index :phone_configurations, %i[user_id made_default_at created_at]
+    add_index(
+      :phone_configurations,
+      %i[made_default_at created_at],
+      algorithm: :concurrently,
+    )
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema.define(version: 20190529120309) do
+ActiveRecord::Schema.define(version: 20190604110233) do
 
   # These are extensions that must be enabled in order to support this database
   enable_extension "plpgsql"
@@ -200,7 +200,7 @@
     t.datetime "created_at", null: false
     t.datetime "updated_at", null: false
     t.datetime "made_default_at"
-    t.index ["made_default_at", "created_at"], name: "index_phone_configurations_on_made_default_at_and_created_at"
+    t.index ["user_id", "made_default_at", "created_at"], name: "index_phone_configurations_on_made_default_at"
     t.index ["user_id"], name: "index_phone_configurations_on_user_id"
   end