Suggestion: Easier support for publishing posts some time after they're written

I searched for this request but didn't see it anywhere specifically; if I missed, please feel free to link & close.

**Is your feature request related to a problem? Please describe.**

I have a number of posts that I batch up for future release. I don't have a set queue necessarily. So when I move an article out of review and publish it, it may show up earlier than other articles due to the date slug, even though it's been published after.

As a result, I can only use Netlify until the final step, when I have to drop into the git branch, rename the file, and merge it manually.

I don't underestimate the complexities that could be involved in this, but resolving this would make it possible for me to use Netlify CMS for the entirety of my publishing workflow (and that would be awesome!)

**Describe the solution you'd like**

Given I have previously drafted a post
And it is in my workflow
When I open the post
And in the course of editing, I update the date field of the post
And I save the post
Then update the slug in the filename to reflect the updated date

Given I have a post that has already been published
When I edit the post
And I don't update the date
And I save the post
Then do not update the slug in the file name

**Describe alternatives you've considered**

I've had difficulty coming up with alternatives, but I am certainly open to them.

My current workaround to drop into the PR in git, rename the file, and then manually merge. Which certainly is OK if this feature isn't implemented; it just forces me to drop out of the Netlify CMS experience in order to accomplish my goal.

**Additional context**

I am currently using Jekyll for publishing my blog, and that is what I'm integrating with Netlify CMS.

Thanks for considering! Absolutely love this project.