[SDTEST-1345] Add Datadog RUM integration support for browser tests with cuprite driver

[anmarchenko]

What does this PR do?
Adds Datadog RUM integration for browser tests using cuprite browser driver

Motivation
Feature request from a customer

How to test the change?
I tested it by creating a test driven by cuprite that looks like that:

require_relative "helper"

class CupriteTest < CapybaraTestCase
  def test_visit_datadog_home_page
    visit "https://app.datadoghq.com/"
    assert page.has_content?("Datadog")
  end
end

Browser-specific tags are correctly added to the test:

RUM session is connected to the test: