Release managers shouldn't have to come up with Tweets for releases

Right now our Tweet templates for (security) releases are as follows:

!tweet "GitLab 11.5.10 is released! BLOG_POST_URL DESCRIPTION OF THE CHANGES"

A release manager should not have to come up with the exact message, instead we should just provide a message that can be copy-pasted directly (minus having to manually add the blog post URL).