Add a way for the user to copy the default/suggested sitename during create new site flow

[AmandaRiu]

while creating a new site, the user is presented with a screen containing the suggested/default sitename, and an option to change it. If the user is using some sort of 3rd party password management and decides to keep the sitename suggested, they have to manually enter in this name which can be tedious. Would be nice if there was a button to copy that sitename right from the screen.