Add `Log` as Default Alert Destination Type

[Ethen]

Problem

Currently, our alerting system supports various alert destination types such as email, SMS, and webhook. However, we have received a requirement to include a new default alert destination type called Log. When Log is selected as the alert destination, the alert should be generated as a debug log entry.

Proposed Solution

Introduce a new default alert destination type called Log that just emits a log message from the alerting subsystem to represent an alert invocation.