[AMQ-9537] Update user-guide.html

[AlexejTimonin]

Updated things I've noticed that did not work when following the guide:

• Windows example of starting the broker did not work. The broker on windows can be started with activemq.bat start
• Removed the mentions of ANT in the guide, the ANT examples were removed in 5.16.0
• Updated instructions on how to start the broker on windows with web apps.
• Starting broker with the demo apps did not work, updated the configuration to use the config the broker ships with, ~saved the 5.x demo config for reference.~
• Updated in the guide where to change the default credentials.