title: Add pearsonr mc, update functionality to match the original docs
comments: _The documentation is not available anymore as the PR was closed or merged._ thank you @lhoestq!! :hugs: 
body: - adds pearsonr metric card
  - adds ability to return p-value
      - p-value was mentioned in the original docs as a return value, but there was no option to return it. I updated the _compute function slightly to have an option to return the p-value.