[deploy-slack-message] Use environment variable for slack notifications
[deploy-slack-message] Use environment variable for slack notifications

ministryofjustice/defence-request-service-auth,ministryofjustice/defence-request-service-auth,ministryofjustice/defence-request-service-auth,ministryofjustice/ds-auth,ministryofjustice/ds-auth,ministryofjustice/ds-auth,ministryofjustice/ds-auth,ministryofjustice/defence-request-service-auth