Fix broken link on Capella alerting reference page

The link to the alert integration in the third bullet point of the metric based alerts section is:

https://docs.couchbase.com/cloud/reference/alert-reference.html#monitoring/alert-integration.adoc

This link for me just stays on the alert-reference page. Instead it should probably be replaced with https://docs.couchbase.com/cloud/clusters/monitoring/alert-integration.html which is linked to later on in the page.