Add CMS type tags to the Astro CMS guide

[udit-001]

I wanted to suggest a small documentation enhancement for the CMS guide:
https://docs.astro.build/en/guides/cms/

Similar to the deployment guide, it would be very helpful to surface high-level “tags” or labels for each CMS option that describe the type of CMS it is, for example:

• Headless (API-based)
• Git-backed (e.g., Netlify CMS–style)
• SaaS vs self-hosted
• Database-driven vs file-based

There are many CMS options listed, and while that’s great, it’s currently difficult to understand these distinctions without opening each CMS’s documentation individually. Adding lightweight tags or categories on the overview page would make it much easier for users to quickly narrow down and choose an option that fits their workflow.

[sarah11918]

We've thought about something like this before to indicate Git-based as that's really the main criteria I've heard people want to decide based on, and we do have prior art for this in our deploy guides menu. There's not a lot of room for multiple tags (especially as none of these are short words!) and this quickly gets cluttered if we try to do too much.

But, I think maybe one optional tag like git-based that only exists on some icons might be a reasonable compromise. It seems like maybe that is the main distinguisher that could be the most useful? (Otherwise, by default, most CMSs are similar in nature, and they could be unmarked.)

It's not really our job to document how all these CMSs work, and keeping up with these pages is already a lot of maintenance. 😅 But if someone would like to try to imitate our deploy guide logic with a tag to indicate one popular tag (I'd assume Git-based? Is there a better candidate than that?) as a proof of concept, we could see what it looks like and consider it!