MediaHelper should not perform loading & logic in its constructor

Problem/Motivation

As outlined in this blog post it's problematic to perform logic and loading in a constructor, and in particular in a service that is always initialized in Drupal.

The MediaHelper service currently does load a configuration object in its constructor, and this should be changed.

Proposed resolution

There are a few options. One would be to move the logic currently performed in the constructor into other helper method(s). Another would be to make media_helper a lazy service.

Either approach would likely have consequences for any code extending the MediaHelper class, but that probably can't be helped when solving this.

Remaining tasks

Decide on an approach to moving the logic currently in the constructor.
Implement it.

API changes

TBD