Add conditional validation to ProductRatePlanChargeTier.price

Problem

As part of Product catalog sync is failing due to blank pr... (#10885 - closed) we remove the presence validation for Zuora::Local::ProductRatePlanChargeTier.price and the not null constrain from its respective database column.

While the Zuora schema specifies that the price attribute is required it looks like this isn't the case given some errors that we get recently.

From this comment:

It looks like there could be different scenarios when we should validate the price attribute. We must validate the price attribute when the charge is a flat fee, or the price of each unit in the tier if the charge model is tiered pricing. We do allow null values in the price column https://gitlab.com/gitlab-org/customers-gitlab-com/-/blob/4b72e82dcfe5f60a67333a531e1fcf642105f8ff/app/models/zuora/local/product_rate_plan_charge_tier.rb#L17.

Proposal

1. Determine all the circumstances where the price attribute is required.
2. Include a conditional presence validation for ProductRatePlanChargeTier.price aligned with 1.

Related issues

• #10885 (closed)