Adding unified streamable notifications

app/controllers/api/v1/notifications_controller.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+class Api::V1::NotificationsController < ApiController
+  before_action -> { doorkeeper_authorize! :read }
+  before_action :require_user!
+
+  respond_to :json
+
+  def index
+    @notifications = Notification.where(account: current_account).with_includes.paginate_by_max_id(20, params[:max_id], params[:since_id])
+
+    next_path = api_v1_notifications_url(max_id: @notifications.last.id)    if @notifications.size == 20
+    prev_path = api_v1_notifications_url(since_id: @notifications.first.id) unless @notifications.empty?
+
+    set_pagination_headers(next_path, prev_path)
+  end
+end