Monitor status of backup buckets.

Configuration options:

• GS_BUCKETS Google Cloud Storage backup buckets to monitor
• EMAIL_HEALTH_CHECK E-mail address for health check status updates.
• EMAIL_ALERT E-mail address for alerts when backups have done been made (E.g. Pagerduty inbound).
• POSTMARK_API_KEY Postmark API key.
• POSTMARK_FROM Postmark sender address.
• ENVIRONMENT Name of environment (e.g. staging)