Support for CloudFormation Stack alpha quality (create/delete only)

[gmichelo]

Description of your changes

1. Generated APIs and controller for cloudformation.Stack resource.
2. CloudFormation Describe API returns "ValidationError" code when the Stack does not exist, hence the expection in generator-config.yaml.
3. Update is not supported yet.

Fixes: #1457

I have:

• [x] Read and followed Crossplane's contribution process.
• [x] Run make reviewable test to ensure this PR is ready for review.

How has this code been tested

Try to manually create a stack resource:

cat > cf-stack.yaml  <<EOF
apiVersion: cloudformation.aws.crossplane.io/v1alpha1
kind: Stack
metadata:
  name: cloudformation-stack-test
spec:
  forProvider:
    stackName: cloudformation-stack-test
    region: us-east-1
    templateBody: |
        {
            "Resources": {
                "VPC": {
                    "Type": "AWS::EC2::VPC",
                    "Properties": {
                        "CidrBlock": "10.2.0.0/16",
                        "EnableDnsSupport": true,
                        "EnableDnsHostnames": true,
                        "Tags": [
                            {
                                "Key": "Name",
                                "Value": {
                                    "Fn::Join": [
                                        "",
                                        [
                                            {
                                                "Ref": "AWS::StackName"
                                            },
                                            "-VPC"
                                        ]
                                    ]
                                }
                            }
                        ]
                    }
                }
            }
        }
EOF

kubectl apply -f cf-stack.yaml

Then check that (1) the Stack is created on your AWS account and (2) the stack resource has synced:

kubectl get stacks

NAME                        READY   SYNCED   EXTERNAL-NAME
cloudformation-stack-test   True    True     cloudformation-stack-test