add warnings as comments to pull requests

Hi,

currently pytest-azurepipelines reports warnings that occur during the tests here:
https://github.com/Azure/pytest-azurepipelines/blob/025be9a383ac19e7543602a1a31ae0cb3f363601/pytest_azurepipelines.py#L207

For my projects I would like to also automatically add comments on PRs, such that in order to complete a PR where warnings occured during the CI run, a developer would need to click the "resolved" button, or even better, fix the code.

This could be done via the [pull request rest api](https://learn.microsoft.com/en-us/rest/api/azure/devops/git/pull-request-thread-comments/create?view=azure-devops-rest-5.1&tabs=HTTP).
Here is also an [example on how to use this rest api using azure dev ops pipeline variables](https://stackoverflow.com/questions/60048492/how-to-create-a-comment-in-azure-devops-pr-in-case-of-build-failure)

Of course it should only happen if explicitly asked for via another command line option.

I could file a PR for this feature if the maintainers of this repo approve the idea.