Add endpoint for room creation

lib/matrix_server/room_server.ex

@@ -0,0 +1,27 @@
+defmodule MatrixServer.RoomServer do
+  use GenServer
+
+  alias MatrixServer.{Repo, Room}
+  alias MatrixServerWeb.API.CreateRoom
+
+  def start_link(_opts) do
+    GenServer.start_link(__MODULE__, :ok, name: __MODULE__)
+  end
+
+  def create_room(params) do
+    GenServer.call(__MODULE__, {:create_room, params})
+  end
+
+  @impl true
+  def init(:ok) do
+    {:ok, %{}}
+  end
+
+  @impl true
+  def handle_call({:create_room, %CreateRoom{} = api}, _from, state) do
+    Room.create(api)
+    |> Repo.transaction()
+
+    {:reply, :ok, state}
+  end
+end