Add OnConnect plugin

Use this plugin to run IRC commands upon connecting to the server.

Signed-off-by: Alek Ratzloff <alekratz@gmail.com>

lib/contrib/on_connect.ex

@@ -0,0 +1,15 @@
+defmodule Omnibot.Contrib.OnConnect do
+  use Omnibot.Plugin
+  require Logger
+
+  @default_config [channels: :all, commands: []]
+
+  @impl true
+  def on_msg(irc, msg) do
+    if msg.command == "001" do
+      Logger.debug("Got welcome message")
+      cfg()[:commands]
+      |> Enum.each(fn [cmd | params] -> Irc.send_msg(irc, cmd, params) end)
+    end
+  end
+end