Remove redundand security group rules

I wrongly assummed that they work like a firewall rules and I thought if
we make a request to particular port from random port we need to allow
connections back. It's not true. It seems security group rules are
applied to connection creation not to literal data flow.

Give space for cluster to power down a node

Upgrade terraform-aws-modules/rds/aws module to 3.3.0

3.1.0: https://github.com/terraform-aws-modules/terraform-aws-rds/releases/tag/v3.1.0
3.2.0: https://github.com/terraform-aws-modules/terraform-aws-rds/releases/tag/v3.2.0
3.3.0: https://github.com/terraform-aws-modules/terraform-aws-rds/releases/tag/v3.3.0

Make it possible to mount secrets as volumes

Use `mount_secrets` within service definition:
	mount_secrets = {
		secret-name = "/destination/path"
	}

Every key in `data` in secret become a file in the destination path.

Multiple ingresses may have single ip

Update example to use new module arguments

Add very first version of do/k8s and k8s/basic modules