Don't update old blogs, and possibly warn readers

[chalin]

I think that we need to define an update policy for blogs. It is understood that blog entries, in contrast to doc pages, are fixed in time -- they rot. For example, Kubernetes doesn't allow updates for blogs older than 12 months. In fact, I implemented the addition of the following banner-warning support (PR#31594) (screenshot from K8s):

We could implement something similar here -- WDYT? I'd keep it simple and only permit the update of blog post in the current year.

Of course, when pages move or are deleted from the website, we can fix any blog posts to ensure that links are still valid (or add a link-checker ignore rule).

Context, this was prompted by the merge of the following PR, which updates a blog entry over a year old:

• Update NGINX instrumentation versions. #3484

Tasks

• Add warning banner
• Don't check external links?

[svrnm]

https://github.com/kubernetes/website/blob/d0cf73f310eedb198203a6109fd8accfac60e954/layouts/blog/baseof.html

This is how Kubernetes is doing it. If I understand it correctly we would need to take the baseof for blog posts out of docsy and modify it, I would rather prefer not doing that.

I wonder if this is a feature we can upstream to docsy?

[chalin]

Thanks for creating the issue over on the Docsy repo. I'll see if we can get this setup more quickly here first though.