feat: add .toBeJsonMatching(expectation) matcher

[Belema]

What

This adds support for a new custom matcher .toBeJsonMatching(...).

Why

This matcher is useful when one wants to check that a function has been called with a JSON string that satisfies some constraints,

expect(fn).toHaveBeenCalledWith(
  expect.toBeJsonMatching({ key1: 'value1' })
);

Housekeeping

• [x] Unit tests
• [x] Documentation is up to date
• [x] No additional lint warnings
• [x] Typescript definitions are added/updated where relevant