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

[roji]

@JoasE thanks for your reviewing and comments. I've copied the content from here into #5256 and done various adjustments - #5256 should now contains all our documentation for preview.1. Can you please take another holistic look and ensure the Cosmos stuff looks good to you?

I'll go ahead close this PR.