Add label definition to add function for LabeledTask

[habibhaidari1]

Description

I really liked the changes in #277 and would like to provide additional functionality. With this changes it is possible to add a label_definition and clear all labels from the task. I added the clear function to make the component in line with the other components like the attribute ruler e.g.
https://github.com/explosion/spaCy/blob/d717123819fb02cf81dcc26be305c0f9cd9893bf/spacy/pipeline/attributeruler.py#L102

Types of change

new feature

Checklist

• I confirm that I have the right to submit this contribution under the project's MIT license.
• I ran all tests in tests and usage_examples/tests, and all new and existing tests passed. This includes
  • all external tests (i. e. pytest ran with --external)
  • all tests requiring a GPU (i. e. pytest ran with --gpu)
• My changes don't require a change to the documentation, or if they do, I've added all required information.

[habibhaidari1]

Sorry for the inconvenience. Pytest skipped the tests on my local machine because there was no API key stored there. I adjusted the test-case to catch non working label_definitions by adding a definition that slightly contradicts the label.

[rmitsch]

Hi @habibhaidari1, thanks for your PR! We'll have a look and give some feedback shortly.

[rmitsch]

Looks good overall, thanks! Can you run black on this? Ha, good timing.

[rmitsch]

I'll go ahead and merge this, as the new test passes locally (and fails here due to the absence of the OpenAI API key in your repo).

Thanks for the contribution! 🎉 This will be part of the next patch release.