ch04/event_listener/MyEventListener should name the png file with URL information embeded

[kazurayam]

ch04/event_listener/MyEventListener will write file like

2023.11.01_19.19.45.922-2c03ff984ab70779f76ed09287a71e32.png

This file name is poor.

It does not encode the URL information from which the PNG images was taken out of. It should have at least the host name and the path taken out of the target URL "https://bonigarcia.dev/selenium-webdriver-java/", for example:

bonigarcai.dev_selenium-webdriver-java.2023.11.01_19.19.45.922.png

This file name looks better to me.