Make events more user friendly

[napravicukod]

It would be good to make events available for non-tech people in order to make them easier to use.
For instance, there could be a list of available events mapped into something like:

[
    'Example.CREATED' => 'backend\models\Example::EVENT_AFTER_INSERT',
    // ...
]

This could be added to app config inside this component.

This way, events could be offered to user as a dropdown list or something similar.

This could be an option for when web hooks are managed by people who are not familiar with code.