Fix RegexEntityExtractor subclass loading

[Mazyod]

Proposed changes:

• RegexEntityExtractor load method instantiates the component using the hardcoded class type as oppose to the cls argument, which loses the subclass type. This caused issues when subclassing RegexEntityExtractor.

Status (please check what you already did):

• added some tests for the functionality
• updated the documentation
• updated the changelog (please check changelog for instructions)
• reformat files using black (please check Readme for instructions)

[sara-tagger]

Thanks for submitting a pull request 🚀 @JustinaPetr will take a look at it as soon as possible ✨

[wochinge]

Thanks for your contribution! 💯
Can you please add a changelog and fix the failing tests? (sorry our docstring checks always capture a bit of the surrounding code to make sure we make progress on improving them).

[wochinge]

Sweet, thank you! 💯