Docs: Get title of the document from the markdown content header

[EngincanV]

Currently, the title of the page is using the file path for the related page. For example, when this page being rendered, the title become as follow:

For this case, it would be better to set the title as Getting-Started-with-the-MAUI. Therefore, we can try to get the h1 header from the content and use it as the title if it exists, otherwise, we can use the current approach and use and normalize the file path and use it as the title.

[ebicoglu]

If it's a markdown document, get it from the first line (if it starts with #)
if it's an HTML document, get it from the first line (if it starts with <h1>)