Query helpers

[sjelfull]

Is your feature request related to a problem? Please describe.
It would be awesome if we could have query helpers for common tasks where it would require you to either opt for very unoptimized queries (if even possible for a big chunk of people to write), or to write manual SQL queries.

Examples:

• Does anyone know if it's possible to query order line items by their status? Am trying to put together a report of any ordered items that have a "Back Ordered" status and am struggling to find any documentation on it. The end goal is a page/report/daily email summary of any items with X status where there's actually some in stock. The idea is to solve the issue of long term out of stock items coming in to stock and noone realising there's an outstanding order for them

Describe the solution you'd like
Something like query helpers that look like this: ```twig
{% set query = craft.commerce.orders().withLineItems().withProductStatus('Back Ordered') %}

Or perhaps Twig filters. We will see.

**Describe alternatives you've considered**
No alternatives exist today.