Add code to terminate the Grid servers

[sbabcoc]

In Selenium 4, grid server "lifecycle" features have been removed. To shut down servers in Selenium 4 Grid, we'll need to determine the process ID of each server and use ProcessHandle to shut it down. To do this most gracefully, we need to figure out if we can add metadata to each server process to indicate its role and port, in the same way that we flag Appium servers running under PM2.