Add the release category to all release blog posts

This will enable a category of releases under https://about.gitlab.com/blog/categories/release

Enabled an automatic merge when the build for db00d9fb succeeds

mentioned in issue #721 (closed)

Status changed to merged

mentioned in commit 6c7dfe7c

@axil this closes #524 (closed) right?

@virtuacreative true! can you maybe respond to that comment with a link to the release category?

mentioned in issue #524 (closed)

Axil, done!

Mentioned in commit 6c7dfe7c