[rb] allow users to direct driver process output

[titusfortner]

Description

Allow users to specify where driver log output goes

Motivation and Context

Currently output is discarded unless the logger level is set to :debug, then all the driver logs are included in the all the Selenium logs

Examples:

Selenium::WebDriver::Service.chrome(log: '/path/to/chromedriver.log')

Selenium::WebDriver::Service.chrome(log: :stdout)

Selenium::WebDriver::Service.chrome(log: :stderr, args: ['--verbose'])