feat: Add nginx:show-conf command

Closes #3552

plugins/nginx-vhosts/subcommands/show-conf

@@ -0,0 +1,20 @@
+#!/usr/bin/env bash
+set -eo pipefail
+[[ $DOKKU_TRACE ]] && set -x
+source "$PLUGIN_CORE_AVAILABLE_PATH/common/functions"
+
+nginx_show_conf_cmd() {
+  declare desc="display app nginx conf"
+  declare cmd="nginx:show-conf" argv=("$@")
+  [[ ${argv[0]} == "$cmd" ]] && shift 1
+  declare APP="$1"
+  verify_app_name "$APP"
+
+  if [[ ! -f "$DOKKU_ROOT/$APP/nginx.conf" ]]; then
+    dokku_log_fail "No nginx.conf exists for $APP"
+  fi
+
+  cat "$DOKKU_ROOT/$APP/nginx.conf"
+}
+
+nginx_show_conf_cmd "$@"