Update documentation for Config Split 2.x

I agree with @rbrandon, it's hard to decide which version to use.
A breaf list of changes at least.

This is probably a related issue.

This support issue contains a lot of useful information and is almost a full documentation page by it's own 💬 Config split with pull Active . I include it here, as it might be a great resource for the 2.x related documentation.

RE #5 Use 2.x :D it is not hard, 1 < 2

There is a lot of information in the Drupalcon Europe 2021 presentation about Config Split 2.x.

Thanks @steinmb for linking issues with comments that can serve as a start for documentation.

(I am removing a tag, since tags should not duplicate what already selected for the Component field. I apologize for bumping this issue.)

It doesn't seem like the documentation has changed at all? The video is no substitute as always, but I found it difficult to follow in its own right. It seemed useful for people who already understood everything about the previous version of the module.

What is "stackable"? Is that explained anywhere?
What is the partial split? Why would you use it? Are there any examples?

Trying to find any examples of the most basic cases, like having the Devel module enabled automatically on a local development installation, it seems like most writeups say they are for Drupal 10 but are actually documenting the 1.x version of the module. Or maybe not?