Cosmosdb serverless

[amine-mejaouel]

This PR closes #333

Thanks to discussion in #333 and for @dnperfors and @JordanMarr work on the subject, I added the last brick in order to make the serverless work on cosmos db.

The changes in this PR are as follows:

• Update databaseAccounts/* api versions to 2021-04-15
• Add 'serverless' operation to Cosmos builder
  • Using 'serverless' disables previous 'throughput' usages.
  • Likewise, using 'throughput' disables previous 'serverless' usages.cosmosDb

// Per example, the 'throughput' will be ignored, only the 'serverless' will be applied.
cosmosDb {
   name "cosmos-foo"   
   throughput 400<CosmosDb.RU> 
   serverless
}

• Applying 'serverless' in the arm template:
  • adds 'EnableServerless' inside capabitilities
  • adds a location with a location name (without adding it, the template will not work, more details on: CosmosDB - add support for new "serverless" option #333)

I have read the contributing guidelines and have completed the following:

• Tested my code end-to-end against a live Azure subscription.
• Updated the documentation in the docs folder for the affected changes.
• Written unit tests against the modified code that I have made.
• Updated the release notes with a new entry for this PR.
• Checked the coding standards outlined in the contributions guide and ensured my code adheres to them.

If I haven't completed any of the tasks above, I include the reasons why here:

Below is a minimal example configuration that includes the new features, which can be used to deploy to Azure:

cosmosDb {
    name "cosmos-foo"
    serverless
}

[isaacabraham]

Great stuff. I think there's a couple of API surface suggestions that I would like to see that would make the API even more compelling, but the majority of this looks good to go.

[ninjarobot]

@isaacabraham is this ready to merge?

[isaacabraham]

Apologies, I need to review the updates.

[isaacabraham]

This is good to go. I made a few tiny tweaks:

• Removing a when to a proper pattern match (best practice - pattern matches give better guidance for missing cases).
• Replaced Throughput with FeatureFlag on the Account (correctness - Account doesn't need to know about Throughput, just if Serverless is set or not).
• Renamed ProvisionedThroughput to simply Provisioned.
• Added an example in the docs.

[isaacabraham]

@ninjarobot ok, this is good to go from my side. @amine-mejaouel if you would like to confirm that my final tweaks are ok with you, this can go in. Thanks again!

[amine-mejaouel]

It's all good to me,
Thanks @isaacabraham !