sourceAMI Must be Defined in Two Areas if a template JSON is used in AWS bakes

Issue

Rosco supports adding sourceAMI which would serve as the base image for baking a custom AMI.  This setting can be changed/completed from the UI.  However, if a template JSON contains the filter source_ami_filter, the Source AMI would also be based on the filter conditions.

Cause

There are two steps when the Bake process kicks in.

Rosco would validate the sourceAMI defined in the configuration (or from UI) to see if the source AMI exists.  It validates by making a request to Clouddriver, which in turn uses the AWS APIs to determine if the sourceAMI is valid. ---> HTTP GET http://spin-clouddriver.gowri-operator-spin:7002/aws/images/find?q=CentOS+Linux+7+x86_64+HVM+EBS*&account=gowri-aws&region=us-east-1

Once the source AMI is valid, it invokes the packer command with the sourceAMI seen as the variable along with others.  Below is a sample command it invokes. packer, build, -color=false, -var, aws_region=us-east-1, -var, aws_instance_type=t2.micro, -var, aws_source_ami=ami-d7e1d2bd, -var, aws_target_ami=nginx-all-20220427155605-vendor-centos-7, -var, aws_ssh_username=centos, -var, aws_associate_public_ip_address=true, -var, package_type=rpm, -var, packages=nginx, -var, configDir=/opt/rosco/config/packer, -var, aws_subnet_id=subnet-02fd76fd0e0db6662, -var, aws_vpc_id=vpc-0a54022472f8eeb4c, /opt/rosco/config/packer/aws-vendor-centos-7-latest.json

If the sourceAMI is not defined in the Rosco configurations, the bake will fail during the validation step. Users may also have a criteria/filter before fetching the source AMI that uses a prefix.  ``````If the filter is defined, Packer does not respect the variables (such as sourceAMI) passed to the Packer command.  Without the filter, the accurate sourceAMI cannot be located because Spinnaker does not support fields like owners that's available on the filter in the template JSON.