[#1668] Restricted access to app metrics endpoint by default. Added ability to configure IP whitelist for this endpoint.

Added tests and documentation.

lib/pleroma/helpers/inet_helper.ex

@@ -0,0 +1,19 @@
+# Pleroma: A lightweight social networking server
+# Copyright © 2017-2020 Pleroma Authors <https://pleroma.social/>
+# SPDX-License-Identifier: AGPL-3.0-only
+
+defmodule Pleroma.Helpers.InetHelper do
+  def parse_address(ip) when is_tuple(ip) do
+    {:ok, ip}
+  end
+
+  def parse_address(ip) when is_binary(ip) do
+    ip
+    |> String.to_charlist()
+    |> parse_address()
+  end
+
+  def parse_address(ip) do
+    :inet.parse_address(ip)
+  end
+end