ReplaceTable helper should be passed a connection

Update the `ReplaceTable` helper to accept an external database
connection rather than relying directly on
`ActiveRecord::Base.connection`

.rubocop_manual_todo.yml

@@ -2445,7 +2445,6 @@ Database/MultipleDatabases:
     - 'lib/gitlab/database/migrations/observers/query_log.rb'
     - 'lib/gitlab/database/multi_threaded_migration.rb'
     - 'lib/gitlab/database/partitioning_migration_helpers/backfill_partitioned_table.rb'
-    - 'lib/gitlab/database/partitioning/replace_table.rb'
     - 'lib/gitlab/database/postgres_hll/batch_distinct_counter.rb'
     - 'lib/gitlab/database/postgresql_adapter/dump_schema_versions_mixin.rb'
     - 'lib/gitlab/database/postgresql_database_tasks/load_schema_versions_mixin.rb'

lib/gitlab/database/partitioning/replace_table.rb

@@ -9,7 +9,8 @@ module Gitlab
         attr_reader :original_table, :replacement_table, :replaced_table, :primary_key_column,
           :sequence, :original_primary_key, :replacement_primary_key, :replaced_primary_key
 
-        def initialize(original_table, replacement_table, replaced_table, primary_key_column)
+        def initialize(connection, original_table, replacement_table, replaced_table, primary_key_column)
+          @connection = connection
           @original_table = original_table
           @replacement_table = replacement_table
           @replaced_table = replaced_table
@@ -29,10 +30,8 @@ module Gitlab
 
         private
 
+        attr_reader :connection
         delegate :execute, :quote_table_name, :quote_column_name, to: :connection
-        def connection
-          @connection ||= ActiveRecord::Base.connection
-        end
 
         def default_sequence(table, column)
           "#{table}_#{column}_seq"

lib/gitlab/database/partitioning_migration_helpers/table_management_helpers.rb

@@ -428,8 +428,8 @@ module Gitlab
         end
 
         def replace_table(original_table_name, replacement_table_name, replaced_table_name, primary_key_name)
-          replace_table = Gitlab::Database::Partitioning::ReplaceTable.new(original_table_name.to_s,
-              replacement_table_name, replaced_table_name, primary_key_name)
+          replace_table = Gitlab::Database::Partitioning::ReplaceTable.new(connection,
+              original_table_name.to_s, replacement_table_name, replaced_table_name, primary_key_name)
 
           transaction do
             drop_sync_trigger(original_table_name)

spec/lib/gitlab/database/partitioning/replace_table_spec.rb

@@ -5,7 +5,9 @@ require 'spec_helper'
 RSpec.describe Gitlab::Database::Partitioning::ReplaceTable, '#perform' do
   include Database::TableSchemaHelpers
 
-  subject(:replace_table) { described_class.new(original_table, replacement_table, archived_table, 'id').perform }
+  subject(:replace_table) do
+    described_class.new(connection, original_table, replacement_table, archived_table, 'id').perform
+  end
 
   let(:original_table) { '_test_original_table' }
   let(:replacement_table) { '_test_replacement_table' }