docs: use details to condense migration guide

[davidhewitt]

Our migration guide is getting extremely long. I'd like to make it easier for users reading performing just the latest upgrade to easily scan for the content relevant for them.

One option would be to split the migration guide over several pages, but I think any such splitting (other than recent version split from the rest) would be quite arbitrary and also be harder to track.

I propose here to add <details> tags to every section older than the current upgrade, to collapse the content. I also added some styling for these tags so that the list renders in a readable way.

Here's what this looks like on my machine:

[Icxolu]

I like the idea! I'd definitely prefer this over splitting. We could also add those for the current release, but have them expanded by default. That way you could close the ones that you already dealt with or won't affect you. Just something that came to mind, not sure if necessary.

[davidhewitt]

We could also add those for the current release, but have them expanded by default. That way you could close the ones that you already dealt with or won't affect you. Just something that came to mind, not sure if necessary.

I like this! To avoid conflicts with a PR I'm currently writing for #3958, would it be ok to push those tags as part of that PR?

[Icxolu]

would it be ok to push those tags as part of that PR?

I'm fine with that 👍

[davidhewitt]

I think we're happy with this, so I'll proceed to merge.