src: make use of `supplychain.spec.serviceaccountref` to set configure the default controller SA

[cirocosta]

problem description

in the current supplychain, we're passing the default service_account data value to params, but not to supplychain.spec.serviceAccountRef, which has the effect of keeping the use of default as the serviceaccount when it comes to permissions for the controller, but still passing down to the children objects the one that goes via params.

proposed solution

update supplychain.spec.serviceaccountref to point at the same serviceaccount name as the one configured in the package values.

[cirocosta]

ps.: in case someone would want to add this to the current release making use of an overlay:

#@ load("@ytt:overlay", "overlay")
#@ load("@ytt:data", "data")

#@overlay/match by=overlay.subset({"kind":"ClusterSupplyChain"}),expects="1+"
---
spec:
  #@overlay/match missing_ok=True
  serviceAccountRef:
    #@overlay/match missing_ok=True
    name: #@ data.values.service_account

ala

apiVersion: data.packaging.carvel.dev/v1alpha1
kind: Package
metadata:
  name: cartographer-catalog.community.tanzu.vmware.com.0.3.0
spec:
  refName: cartographer-catalog.community.tanzu.vmware.com
  releasedAt: "2022-04-13T17:50:24Z"
  template:
    spec:
      deploy:
      - kapp: {}
      fetch:
      - imgpkgBundle:
          image: projects.registry.vmware.com/tce/cartographer@sha256:1657d88fc1d1492af7d92f12f9b3851342f6b5f119901057b7251c441192c83a
      template:
      - ytt:
          ignoreUnknownComments: true
          inline:
            paths:
              default-service-account.yaml: |
                #@ load("@ytt:overlay", "overlay")
                #@ load("@ytt:data", "data")

                #@overlay/match by=overlay.subset({"kind":"ClusterSupplyChain"}),expects="1+"
                ---
                spec:
                  #@overlay/match missing_ok=True
                  serviceAccountRef:
                    #@overlay/match missing_ok=True
                    name: #@ data.values.service_account
          paths:
          - config
      - kbld:
          paths:
          - .imgpkg/images.yml
          - '-'
# ...

for a carvel package