Add option to allow using the browser's default context

This would grant access to persistent state such as cookies that are
associated with the default browser profile.

lib/ferrum/browser.rb

@@ -125,6 +125,9 @@ class Browser
     # @option options [Hash] :env
     #   Environment variables you'd like to pass through to the process.
     #
+    # @option options [Boolean] :use_default_context
+    #   When true, allows using the default browser context that has access to the browser's persistent state.
+    #
     def initialize(options = nil)
       @options = Options.new(options)
       @client = @process = @contexts = nil

lib/ferrum/browser/options.rb

@@ -15,7 +15,7 @@ class Options
                   :js_errors, :base_url, :slowmo, :pending_connection_errors,
                   :url, :ws_url, :env, :process_timeout, :browser_name, :browser_path,
                   :save_path, :proxy, :port, :host, :headless, :browser_options,
-                  :ignore_default_browser_options, :xvfb, :flatten
+                  :ignore_default_browser_options, :xvfb, :flatten, :use_default_context
       attr_accessor :timeout, :default_user_agent
 
       def initialize(options = nil)
@@ -45,6 +45,7 @@ def initialize(options = nil)
         @base_url = parse_base_url(@options[:base_url]) if @options[:base_url]
         @url = @options[:url].to_s if @options[:url]
         @ws_url = @options[:ws_url].to_s if @options[:ws_url]
+        @use_default_context = @options.fetch(:use_default_context, false)
 
         @options = @options.merge(window_size: @window_size).freeze
         @browser_options = @options.fetch(:browser_options, {}).freeze

lib/ferrum/contexts.rb

@@ -11,7 +11,7 @@ class Contexts
     def initialize(client)
       @contexts = Concurrent::Map.new
       @client = client
-      @default_context = create_default_context
+      @default_context = create_default_context if @client.options.use_default_context
       subscribe
       auto_attach
       discover