Create Blogpost PR Template and Docs

[jdrueckert]

Task

Create a PR template (see GitHub Docs) for new blog posts. This template should include guidance on naming the PR, which information to provide, and which labels to add.

Further, add information to the blog post author docs on how to create a new PR with the template.

The PR template could also include which to ping for review. However, that's always hard due to fluctuation. Maybe a GitHub team would be the better choice as that can be pinged and allows reaching the currently active contributors of that field (if the teams are properly managed).