Add the code names to alert for better searchability

Summary: When searching for an alert code like "auto_failover_node" or Google or otherwise, no relevant documentation is found.

Example: Search for "auto_failover_node" on docs.couchbase.com or on google. There aren't any results that really tell a reader what that code means (although that particular code is relatively understandable).

Recommendation: A list of these codes should be present somewhere in the documentation with descriptions and/or links for more information. One place that might be good is: https://developer.couchbase.com/documentation/server/current/settings/configure-alerts.html in the "Available Alerts" table. Maybe add a third column with the actual code?