feat: add public destroy command for resetting mynah ui state

[jpinkney-aws]

Problem

When running e2e tests in vscode against mynah ui you have two options:

1. Create one mynah ui instance for all the subsequent tests, but this doesn't allow you to test specific functionality (e.g. the welcome page in VSCode shows up 3 times)
2. Create one mynah ui instance per test, but since mynah ui uses singletons and the module has been initialized already, its not actually providing a fresh state causing multiple extra events to be sent that shouldn't be

Solution

Add a destroy method for resetting all the singletons back to their initial state. This allows you to create a fresh mynah ui instance in every test

Tests

• I have tested this change on VSCode
• I have tested this change on JetBrains

License

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[Jurredr]

Some small nits in documentation, otherwise approved. Nice addition.