Centralize the logic that looks at the latest organic traffic data and computes CPC

**Is your feature request related to a problem? Please describe.**
Related to: https://github.com/adobe/spacecat-audit-worker/pull/725

**Describe the solution you'd like**
In the future, we'll have to centralize the logic that looks at the latest organic traffic data and computes CPC, as this is now also in https://github.com/adobe/spacecat-api-service/blob/e0e3d1e2310636055b037d24d8ddc038114e31bb/src/controllers/sites.js#L423-L439 and https://github.com/adobe/spacecat-import-worker/blob/e0ae0953ae33aac5775a7e2a9a5d954553f35a36/src/mapper/latest-metrics.js#L30-L35

比较 spacecat-api-service/src/controllers/sites.js 中第 423-439 行附近引用的逻辑与 spacecat-import-worker/src/mapper/latest-metrics.js 中第 30-35 行附近的逻辑，以及相关的 spacecat-audit-worker pull request。在定义集中式实现和完整迁移应包含哪些内容之前，确定共享入口点和预期消费者。

由索引模型根据 Issue 内容生成。