3-stage build job

During the discussion(https://github.com/kernelci/kernelci-pipeline/issues/330) of kbuild fragments we came to conclusion we need to implement 3-stage kernel build job:

1. Prepare job (generate config fragments, shell script with compile commands), run in kernelci/kernelci container
2. Compile job (compile kernel), run in compiler specific container
3. Complete job (upload artifacts, send notifications), run in kernelci/kernelci container

After initial investigation i found it is possible in k8s following way:

apiVersion: v1
kind: Pod
metadata:
  name: sequential-job
spec:
  restartPolicy: Never
  volumes:
  - name: shared-data
    emptyDir: {}
  # these run sequentally
  initContainers:
  - name: job-1
    image: kernelci/kernelci
    command: ['sh', '-c', 'prepare-kbuild.sh','nodeid','jobid']
    volumeMounts:
      - name: shared-data
        mountPath: /generated
  - name: job-2
    image: kernelci/compiler-gcc2055.1
    command: ['sh', '-c', '/generated/compile.sh']
    volumeMounts:
      - name: shared-data
        mountPath: /generated
  # syntax require to have one from "containers"
  # it will run only after all initContainers are finished
  containers:
  - name: job-3
    image: kernelci/kernelci
    command: ['sh', '-c', 'complete.sh','nodeid','jobid']
    volumeMounts:
      - name: shared-data
        mountPath: /generated  

Ignore script names, type, nodeid and jobid, it is just example for now

Start by reading this issue alongside the linked discussion in issue #330, then inspect how the existing pipeline represents kernel build jobs. Use the Kubernetes Pod example as the proposed execution model, and consider the work complete when preparation, compilation, and completion run sequentially in their specified containers with shared generated data and artifact handling.