Add documentation for cosmos db provider transactional batches

[JoasE]

Adds documentation for the usage of TransactionalBatch in the Cosmos DB provider when saving changes.
See: dotnet/efcore#17308 and dotnet/efcore#36693

[JoasE]

Should probably only be merged once 11.0 is out? I could not find a 11.0 or release branching strategy in the repo and the contributing guide said to target main (I only found live)

[roji]

Thanks for writing docs on this - that's much appreciated, even if quite early given this feature hasn't been merged yet and won't appear until EF 11 😅 I'm worried that additional PR changes/design discussions may still change some details which would require changing the docs again.

In any case, see below for some review comments.

[JoasE]

@roji You're right! Sorry about that, should have probably at-least kept it as draft until the other PR was merged. Will do that now. I had some time left over so didn't mind working ahead a bit and making changes later if needed. Thank you for reviewing despite that!

[roji]

Hey @JoasE, the EF 11 preview.1 release is coming up in around a week, and it would be nice to get the docs done and merged in. Do you want to finish work on this in the next few days? If not I can take over and finish.

Also, I think this is something that's worth mentioning in the 11.0 what's new docs. I've pushed a preview-1 branch which contains a stub for the new what's new page where you can add a note with a minimal example. Nothing too big - I generally like the what's new page to be the minimum needed to get the idea of the feature across, and then a link to the proper doc page for those who are fully interested.

Let me know!

[roji]

@JoasE I've also just submitted #5256, which documents all other preview-1 features (including the two other Cosmos features you contributed) - a review on it would be much appreciated. Based on your answer for the above I can do the same for transaction batches, or you can finalize work here yourself and target the preview-1 branch - let me know.

[JoasE]

@roji I think it would be easier if you continued on this if that is not an issue? Might be easier to get general tone/wording/structure more aligned.

[JoasE]

I can do a double check on the factual correctness of this possibly later today or tomorrow

[JoasE]

This is all still correct, but it does fail to mention the 2MB limit introduced in dotnet/efcore/#36903