[ADD] Optional tags

[ovcharenko]

Adding optional tags to follow AWS best practices

There are few PRs that must be completed before:

• https://github.com/cn-terraform/terraform-aws-ecs-cluster/pull/3
• https://github.com/cn-terraform/terraform-aws-ecs-fargate-task-definition/pull/14
• https://github.com/cn-terraform/terraform-aws-ecs-fargate-service/pull/25