Retrieve conversion rate

Retrieves the conversion rate (CR) for all your searches with at least one conversion event, including a daily breakdown. By default, the analyzed period includes the last eight days including the current day. **There's a difference between a 0 and null CR when `clickAnalytics` is enabled:** - **Null** means there were no queries: since Algolia didn't receive any events, CR is null. - **0** mean there _were_ queries but no [conversion events](https://www.algolia.com/doc/guides/sending-even...