Add alarms for NAT Gateway when BytesOutToDestination is large

A legitimate attack vector consists of causing our applications to produce large payload responses that generate egress charges. Currently NAT Gateways in ca-central charge $0.05 per GB egressed. 1TB costs $50. Constantly generating that much traffic would accumulate costs over time. A simple solution is to package the VPC module with an alarm that measures the total BytesOutToDestination for the NAT in a 24 hour period and alerts if it goes over a reasonable amount (ex. 1 TB).

Locate the VPC module and its NAT Gateway resources, then review how existing alarms or metrics are configured. Determine how to measure total BytesOutToDestination over 24 hours and define the requested threshold; this is done when the module alerts after the specified egress amount is exceeded.

Written by the indexing model from the issue text.