Implement client ban and unban endpoints

lib/matrix_server_web/client/request/ban.ex

@@ -0,0 +1,20 @@
+defmodule MatrixServerWeb.Client.Request.Ban do
+  use MatrixServerWeb.Request
+
+  @type t :: %__MODULE__{
+          user_id: String.t(),
+          reason: String.t() | nil
+        }
+
+  @primary_key false
+  embedded_schema do
+    field :user_id, :string
+    field :reason, :string
+  end
+
+  def changeset(data, params) do
+    data
+    |> cast(params, [:user_id, :reason])
+    |> validate_required([:user_id])
+  end
+end