Add request info to custom_sampling_context in Rails middleware

[linhmtran168]

For rack middleware, it's already implemented in #1749
But since the start_transaction is overridden in Rails middleware, so request info is not available in sampling context when using with Rails app

sentry-ruby/sentry-rails/lib/sentry/rails/capture_exceptions.rb

Lines 33 to 42 in 9f6ab0c

	def start_transaction(env, scope)
	sentry_trace = env["HTTP_SENTRY_TRACE"]
	options = { name: scope.transaction_name, op: transaction_op }
	if @assets_regex && scope.transaction_name.match?(@assets_regex)
	options.merge!(sampled: false)
	end
	transaction = Sentry::Transaction.from_sentry_trace(sentry_trace, **options) if sentry_trace
	Sentry.start_transaction(transaction: transaction, **options)