[📖 esl-core]: documentation for ESLEventListeners module

[ala-n]

As an ESL consumer, I want to have a clear definition of how to use ESLEventListeners and their practical use cases.

It is requested to create a README description for esl-utils/dom/event submodule. Create a public page on a website to render this doc.

Doc should consist of a clear and detailed definition of what is the ESLEventListener, how to use it and snippets of it's useage.