Update instructions for setting up firewall rules on AWS

[QingXXiong]

In src/server_manager/messages/en.json, we have:

  "aws-lightsail-firewall-3": "In the 'Firewall' section, click 'Add another'.",
  "aws-lightsail-firewall-4": "Set 'Application' value to 'All TCP+UDP'.",
  "aws-lightsail-firewall-5": "Click 'Save'.",

But the steps are no longer true for the latest Lightsail. For more info, see Adding and editing instance firewall rules.

The correct and straightforward steps should be:

4. Scroll down to 'IPv6 firewall', then click 'Add rule'.
5. Set 'Application' value to 'All protocols'. 
6. Click 'Create' on the right to save your rule.

I think Set 'Application' value to may be a bit technical and should be For 'Application', select... for a wider user base.