Add new post template (#1983)

Signed-off-by: Shelley Lambert <slambert@gmail.com>

.github/ISSUE_TEMPLATE/blog_post.md

@@ -0,0 +1,20 @@
+---
+name: New blog post 
+about: Create a blog post issue for upcoming shareable content
+title: ''
+labels: documentation
+assignees: ''
+
+---
+
+**Decide on a Blog post title**
+Decide on a descriptive title for your new blog post and reference it in the title of this issue. The pull request to address this issue will have a 'Slugify-ed' version of the blog post title as the directory in https://github.com/adoptium/adoptium.net/tree/main/content/blog. See the instructions at https://github.com/adoptium/adoptium.net/tree/main/content#adding-content for details.
+
+**Determine what content theme this blog post relates to**
+As per https://github.com/adoptium/adoptium.net/issues/1956, there are several themes that a new post can relate to, and this also determines which tags to use for the post.
+
+**Gather supporting images and media**
+Find helpful supporting material to make your new blog post more interesting to read.
+
+**Set a target publish date**
+Each new blog post should have a target publish date that is represented in the [Adoptium Content Streams calendar](https://calendar.google.com/calendar/u/0?cid=MTI5YzA3YzBiMTBiYjBlNmE2N2JkM2U3ODRkYzE5ODA1OWVmMGJmMTkwODBkZDY4MzhjNTZhMDQ3MDM1MWYwZEBncm91cC5jYWxlbmRhci5nb29nbGUuY29t). The date can be revised as needed, this just helps the marketing committee plan better.