CosmosDB: Add the 'EnableServerless' capability to accounts

[Pilchie]

Description

Change Azure Cosmos DB accounts to be created with the "EnableServerless" capability. This is the recommended path for dev/test type scenarios, since it scales to zero when idle. See https://learn.microsoft.com/en-us/azure/cosmos-db/serverless for more details about it.

Fixes #8854

Checklist

• Is this feature complete?
  • Yes. Ready to ship.
  • No. Follow-up changes expected.
• Are you including unit tests for the changes and scenario tests if relevant?
  • Yes
  • No
• Did you add public API?
  • Yes
    • If yes, did you have an API Review for it?
      • Yes
      • No
    • Did you add <remarks /> and <code /> elements on your triple slash comments?
      • Yes
      • No
  • No
• Does the change make any security assumptions or guarantees?
  • Yes
    • If yes, have you done a threat model and had a security review?
      • Yes
      • No
  • No
• Does the change require an update in our Aspire docs?
  • Yes
    • Link to aspire-docs issue (consider using one of the following templates):
      • New (or update) doc-idea template
      • New breaking-change template
      • New diagnostic template
  • No

[Copilot]

Pull Request Overview

This PR adds support for Azure Cosmos DB accounts to be created in serverless mode by introducing a new constant and updating the account configuration with the corresponding capability.

• Added a new constant in CosmosConstants for the serverless capability.
• Updated the AzureCosmosDBExtensions to include the "EnableServerless" capability when configuring Cosmos DB accounts.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
src/Shared/Cosmos/CosmosConstants.cs	Added a constant for the "EnableServerless" capability.
src/Aspire.Hosting.Azure.CosmosDB/AzureCosmosDBExtensions.cs	Configured Cosmos DB accounts to include the serverless capability.

[Pilchie]

@davidfowl - care to take a look? Note this changes it unconditionally for all accounts. If we want to expose configuration I'll need some suggestions on what the right pattern is to do that.

[Pilchie]

Other note: I didn't actually run through provisioning with this. Would be great if someone could test a scenario known to work with Cosmos DB (or point me to one).

[davidfowl]

@sebastienros should we add a WithDefaultSku like we did with sql ?

[Pilchie]

@davidfowl @sebastienros - please take another look.

[davidfowl]

The one question I have is around subscription limitations with the serverless capability. Is it one per sub or something crazy like that?

[Pilchie]

@davidfowl - We don't have subscription limits with the serverless capability. We do have a free account tier that is one per sub, but that is different than this.

[Pilchie]

Do you want me to merge, or do you want to?

[davidfowl]

I was giving @sebastienros a chance to look but I will merge.