Add CEL code for PSP Policies in library

[JaydipGabani]

To-Do list for each policy:

• [ ] Add src.cel file for the policy under src/pod-security-policy/<name>/

• [ ] Modify constraint.tmpl to add CEL engine and move rego under rego engine

  targets:
  - target: admission.k8s.gatekeeper.sh
    code: 
    - engine: K8sNativeValidation
      source:
  {{ file.Read "src/pod-security-policy/<name>/src.cel" | strings.Indent 10 | strings.TrimSuffix "\n" }}
    - engine: Rego
      source:
        rego: |
  {{ file.Read "src/pod-security-policy/<name>/src.rego" | strings.Indent 12 | strings.TrimSuffix "\n" }}
        libs:
          - |
  {{ file.Read "src/pod-security-policy/<name>/lib_exempt_container.rego" | strings.Indent 14 | strings.TrimSuffix "\n" }}

• [ ] Bump minor version on constraint.tmpl by updating metadata.gatekeeper.sh/version annotation.

• [ ] Run make generate-all to generate all relavent files

• [ ] Run make verify-gator-dockerized POLICY_ENGINE=cel && make verify-gator-dockerized POLICY_ENGINE=rego to test changes in local

PSP Policies list to track migration

• [ ] validation/allow-privilege-escalation
• [ ] validation/apparmor
• [ ] validation/capabilities
• [ ] validation/flexvolume-drivers
• [ ] validation/forbidden-sysctls
• [ ] validation/fsgroup
• [ ] validation/host-filesystem
• [ ] validation/host-namespaces
• [ ] validation/host-network-ports
• [ ] validation/privileged-containers
• [ ] validation/proc-mount
• [ ] validation/read-only-root-filesystem
• [ ] validation/seccomp
• [ ] validation/selinux
• [ ] validation/users
• [ ] validation/volumes