Check concurrent issues

[eldimious]

• Scenario 1: When we update status we first try to find -> this can lead to concurrent issues -> we need either pessimistic or optimistic lock or just update
• Scenario 2: Idempotent API -> avoid duplicated orders (we use unique constraint basket_id + proceed events) / payments (proceed events + unique constraint order_id + psp deduplicated key)
• Scenario 3: Multiple uses try to order same product at same time -> pessimistic lock, optimistic lock, database constraint (stock constraint)