add function to add frequently confused intent to intent report

[amn41]

Proposed changes:

Adds extra info to the intent_report.json created by rasa test. Specifically, a key is added to the dict which contains up to 2 other intents with high numbers in the confusion matrix.

Needs tests and types and general polish

output looks like this:

  "meta_inform_problem_bad-link": {
    "precision": 0.0,
    "recall": 0.0,
    "f1-score": 0.0,
    "support": 3,
    "confused_with": {
      "faq": 1,
      "affirm": 1
    }
  }

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)

[wochinge]

Cool feature 👍

One test with a very small confusion matrix (already there) and one with sth like 5x5 would be great

[amn41]

thanks @wochinge ! can you please have another quick look?

[wochinge]

Looks great. Left a couple of stylistic comments, but otherwise good to go 🚀

[wochinge]

one more comment, but this is now ready to go 👍