Replace kafka_ex with brod

lib/kafkaex_lag_exporter/consumer_offset_fetcher.ex

@@ -0,0 +1,38 @@
+defmodule KafkaexLagExporter.ConsumerOffsetFetcher do
+  @moduledoc """
+  Genserver implementation to consume new messages on topic '__consumer_offsets'
+  """
+
+  use GenServer
+
+  require Logger
+
+  @interval 5_000
+
+  def start_link(default) when is_list(default) do
+    GenServer.start_link(__MODULE__, default)
+  end
+
+  @impl true
+  def init(_) do
+    Logger.info("Starting #{__MODULE__}")
+
+    clients = Application.get_env(:brod, :clients)
+    endpoints = clients[:kafka_client][:endpoints]
+
+    Logger.info("Reveived Kafka endpoints: #{inspect(endpoints)}")
+
+    Process.send_after(self(), :tick, @interval)
+    {:ok, %{endpoints: endpoints}}
+  end
+
+  @impl true
+  def handle_info(:tick, state) do
+    consumer_groups = :brod.list_all_groups(state.endpoints, [])
+    Logger.info("Consumer groups state: #{inspect(consumer_groups)}")
+
+    Process.send_after(self(), :tick, @interval)
+
+    {:noreply, state}
+  end
+end