MD025 should support YAML meta block

[amithegde]

https://pandoc.org/MANUAL.html#extension-yaml_metadata_block

YAML meta block is used to provide additional metadata for the markdown document. For example

---
title: my title
author: my name
date: today
---

when there is a title metadata and # with title, MD025 triggers.

[DavidAnson]

This behavior is documented here: https://github.com/DavidAnson/markdownlint/blob/main/doc/md025.md