feat(skaffold): add completion (#11357)

plugins/skaffold/skaffold.plugin.zsh

@@ -0,0 +1,14 @@
+# Autocompletion for skaffold
+if (( ! $+commands[skaffold] )); then
+  return
+fi
+
+# If the completion file doesn't exist yet, we need to autoload it and
+# bind it to `skaffold`. Otherwise, compinit will have already done that.
+if [[ ! -f "$ZSH_CACHE_DIR/completions/_skaffold" ]]; then
+  typeset -g -A _comps
+  autoload -Uz _skaffold
+  _comps[skaffold]=_skaffold
+fi
+
+skaffold completion zsh >| "$ZSH_CACHE_DIR/completions/_skaffold" &|