Explicit dependencies with `depends_on`; `lifecycle` rules: `create_before_destroy`, `prevent_destroy`, `ignore_changes`, `replace_triggered_by`

Most dependencies are implicit, created by references. Occasionally one resource relies on another without using any of its attributes. The classic example is an instance whose application, at boot, calls a cloud API using a role; the instance must wait for the role's permission policy to be attached, but its arguments never reference the policy. depends_on states that hidden dependency explicitly.