async createTier({name, currency, monthly_price, yearly_price}) {
        const result = await tiers.api.add({
            name: name ?? ('Tier ' + this.#generateRandomId()),
            type: 'paid',
            currency: currency.toUpperCase(),
            monthlyPrice: monthly_price,
            yearlyPrice: yearly_price
        });
        return await models.Product.findOne({
            id: result.id.toHexString()
        });
    }
Creates a Ghost tier (product).
@param {object} data
@param {string} [data.name]
@param {string} data.currency
@param {number} data.monthly_price
@param {number} data.yearly_price
@returns {Promise<object>} - The created product object.