fix(scaffold): use default values.yaml

[olblak]

This pullrequest replaces generate the default values file using values.yaml instead of values.d/default.yaml.
In the process I also renamed a few variable to be more consistent with other similar variables.

A scaffolded policy looks like

.
├── CHANGELOG.md
├── Policy.yaml
├── README.md
├── updatecli.d
│   └── default.yaml
└── values.yaml

Test

To test this pull request, you can run the following commands:

 cd pkg/core/scaffold/
go test .
go build -o bin/updatecli .
./bin/updatecli manifest init /tmp/test2/
# Verify 

Additional Information

Tradeoff

Potential improvement