feat(ngrok): add completion plugin (#12826)

plugins/ngrok/ngrok.plugin.zsh

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