Add db:index task which indexes appropriate commodities and headings.
Add db:index task which indexes appropriate commodities and headings.

leftees/trade-tariff-backend,alphagov/trade-tariff-backend,alphagov/trade-tariff-backend,alphagov/trade-tariff-backend,leftees/trade-tariff-backend,bitzesty/trade-tariff-backend,bitzesty/trade-tariff-backend,bitzesty/trade-tariff-backend,leftees/trade-tariff-backend