Make it possible to configure containerSecurityContext for init-containers

[NissesSenap]

Is your feature request related to a problem? Please describe.
I need to be able to define securityContainerContext on the init container to be able to start the grafana-operator on my current cluster due to psp rules that we have globally defined.

Describe the solution you'd like
Use the same containerSecurityContext on the init container that you get from grafana.spec.deployment.containerSecurityContext

kind: Grafana
metadata:
  name: grafana
spec:
  deployment:
    containerSecurityContext:
      allowPrivilegeEscalation: false

to the init container.

Describe alternatives you've considered
Instead of using the same containerSecurityContext we could define a seperate one for the init container. Instead of using additional special config for initContainers directly under grafana.spec, like we do for grafana.spec.InitResources I would suggest creating a grafana.sepc.initContainers and store all initContainer specific config under it.

kind: Grafana
metadata:
  name: grafana
spec:
  initContainer:
    InitResources:
      requests:
        memory: "64Mi"
        cpu: "250m"
    initContainerSecurityContext:
      allowPrivilegeEscalation: false
  deployment:
    containerSecurityContext:
      allowPrivilegeEscalation: false

We could still keep grafana.spec.InitResources to be backwards compatible and defining it would prioritize it over grafana.spec.initContainer.InitResources. But when releasing 4.0 I would suggest removing grafana.spec.InitResources to only have one place to define initResources.

Additional context
When trying to start the grafana-operator on my current cluster I get the following error:

psp-allow-privilege-escalation-container] Privilege escalation container is not allowed: grafana-plugins-init

Existing solutions
N/A

[HVBE]

Automation should have closed this, resolved through #373 👍