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

Compare the logic referenced in spacecat-api-service/src/controllers/sites.js around lines 423-439 and spacecat-import-worker/src/mapper/latest-metrics.js around lines 30-35, along with the related spacecat-audit-worker pull request. Determine the shared entry point and the expected consumers before defining what a centralized implementation and completed migration would include.

Written by the indexing model from the issue text.