Add completion spec: openshift (oc)

Add an oc completion spec for the OpenShift CLI. Since oc is a superset
of kubectl (both Cobra-based, same __complete protocol), this:

- Creates oc.json based on kubectl.json with OpenShift-specific
  subcommands: login, logout, whoami, new-project, project, projects,
  new-app, new-build, start-build, cancel-build, import-image, tag,
  status, rsh, rsync, extract, idle, observe, process, registry, and
  adm (with nested policy, groups, drain, cordon, inspect, top, etc.)

- Creates oc.rs generators that mirror kubectl's but invoke the oc
  binary directly for dynamic completions (resource types, pods,
  deployments, nodes, roles, contexts, clusters, namespaces, and
  Cobra __complete protocol)

- Refactors kubectl.rs to expose shared helper functions
  (kube_cli_script, kube_cli_post_process,
  kube_cli_builtin_complete_post_process) as pub(super) so both
  kubectl and oc generators can reuse them without duplication

- Registers the oc module in generators/mod.rs

Closes warpdotdev/warp#4147
Closes warpdotdev/warp#5073

Co-Authored-By: Oz <oz-agent@warp.dev>

Author: lucieleblanc