Improve S6571 (`no-redundant-type-constituents`): improve doc about intentional violation about sonarjs

[ilia-kebets-sonarsource]

We're not quite sure what to suggest to users.

1. Using redundant types for developer hints is quite convenient if some value can be several predefined types and custom ones like: foo: 'bar' | 'baz' | string.
2. We tried to use JS doc for IDE auto-completion, but it didn't work.

We should find a way on what best to suggest to users that use redundant types for documentation or developer tooling.

[ericmorand-sonarsource]

@ilia-kebets-sonarsource , if this is of some help, there is a very typical usage of types redundancy in the typings of DOM events, and the purpose is to give developers a hint about what events are natively supported (and of course enable IDE autocompletion).

For example:

document.addEventListener('DOMContentLoaded', () => { // valid and auto-completed
    
});

document.addEventListener('foo', () => { // valid
    
});