*: l10n_br_edi_pos, l10n_ke_edi_oscu_pos

The aim of this commit is to make test writing easier, by choosing
easy-to-calculate prices with their corresponding taxes.

The products created have prices of 10 or 20 with taxes of 5, 10 or 15
percent.

A global class will be created and inherited by all Point of Sale tests,
with the aim of always using products already available. If a different
product is required in a specific test, existing products can be
modified.

---

Test in file: `point_of_sale/tests/test_point_of_sale_flow.py`:

- Test `test_order_refund_lots` is removed and adapted in the frontend
tour `test_lot`

- Test `test_order_to_invoice` is removed because frontend is already
testing this behavior, related tests:
    - Test `test_02_pos_with_invoiced`
    - Test `test_order_and_invoice_amounts`
    - And more in submodules...

- Test `test_order_with_deleted_tax` is removed because it is using
`sync_from_ui` method which should not be used in the backend.
Frontend tours are already testing its behavior

- Test `test_order_refund_picking` is merged with `test_order_to_picking`

- Test `test_order_with_different_payments_and_refund` is removed
because its description don't correspond to the actual behavior of the
test. The goal of the test isn't clear.

- Test `test_product_combo_creation` is removed because its already
tested in owner module.

- Test `test_order_refund_with_owner` was merged with the frontend
test `test_lot`

- Test `test_change_is_deducted_from_cash` was merged with the frontend
test `test_tracking_number_closing_session`