Legacy backend implementation does not work with recent versions

[humbleice]

Describe the bug
When using the createRouter method for the legacy backend system, there are errors in the code because RouterOptions require a store and discovery value. As a consumer of the plugin, it isn't clear how to provide these values and it doesn't seem possible to access the classes needed to instantiate the necessary instances.

To Reproduce
Steps to reproduce the behavior:

1. Follow the directions for installing the latest version of the backend plugin using the legacy backend system.
2. The IDE complains when you add the code for the backend/plugins/pagerduty.ts file.

Expected behavior
There is a clear and documented approach for using the legacy backend system with newer versions of the plugin.

Desktop (please complete the following information):

• OS: Linux (WSL)
• Browser: N/A
• Version: 0.7.0-0.9.1

Additional context

• It seems this was introduced in version 7.0
• I also created a ticket here thinking this was a documentation issue.