Replace cdk-watchful with cdk-monitoring-constructs

Compared to cdk-watchful, cdk-monitoring-constructs is more actively maintained, supports creating alarms in addition to dashboards, and works out of the box with more L2 constructs.

https://github.com/cdklabs/cdk-monitoring-constructs

Start by locating all references to cdk-watchful in the construct-hub repository, then review cdk-monitoring-constructs and its compatibility with the existing constructs. Done means the old dependency and integrations are replaced, dashboards and alarms continue to work, and the repository's checks pass.

Written by the indexing model from the issue text.