Improve support for boolean values

[gbonnefille]

When using an HelmChart with a set like:

  set:
    concurrent: 10
    checkInterval: 30
    rbac.create: true

The controller fails with:

E0616 15:09:55.015104    3015 reflector.go:153] github.com/rancher/helm-controller/pkg/generated/informers/externalversions/factory.go:117: Failed to list *v1.HelmChart: v1.HelmChartList.Items: []v1.HelmChart: v1.HelmChart.Spec: v1.HelmChartSpec.Set: unmarshalerDecoder: json: cannot unmarshal bool into Go value of type int32, error found in #10 byte of ...|eate":true,...

I can overpass this issue by forcing the value to string:

set:
  concurrent: 10
  checkInterval: 30
  rbac.create: "true"

I suspect something goes wrong when converting a YAML boolean into JSON.

PS: I'm using K3OS v0.10.2.