FaaS and Pub/Sub terraform module/boilerplate

Description

In order for use to manageable add new event driven/sourced patterns we should package up our FaaS and Pub/Sub functionality.

Acceptance criteria

Pub/Sub

• dead letter queue
• alerts
  • repeated failures of functions
  • dead letter queue not empty

Future features to consider path to achieve

• release snapshots
• additional generic AND topic/function specific alerting
• long term event storage, e.g. piped into BigQuery, partitioned on GDPR concerns