Changing a subscription from non-batchable to batchable doesn't work

[rolfbjarne]

Changing a subscription from non-batchable to batchable results in:

fail: An unexpected error occurred while setting up the base data for ingestion. Please contact an administrator of maestro-configuration.
      System.ArgumentException: Subscription update failed for subscription f4928934-9e75-4ba7-b3d0-757a5edf906b because there was an attempt to modify the following immutable fields: Batchable
         at Maestro.DataProviders.SqlBarClient.UpdateSubscription(Subscription subscription, Subscription existingSubscription)
         at Maestro.DataProviders.SqlBarClient.UpdateSubscriptionsAsync(IEnumerable`1 subscriptions, Boolean andSaveContext)
         at Maestro.DataProviders.ConfigurationIngestion.ConfigurationIngestor.UpdateSubscriptions(IEnumerable`1 updatedSubscriptions, Namespace namespaceEntity, Dictionary`2 existingChannelsByName)
         at Maestro.DataProviders.ConfigurationIngestion.ConfigurationIngestor.PerformEntityChangesAsync(IngestedConfigurationUpdates configurationDataUpdate, Namespace namespaceEntity)
         at Maestro.DataProviders.ConfigurationIngestion.ConfigurationIngestor.IngestConfigurationAsync(ConfigurationData configurationData, String configurationNamespace, Boolean saveChanges)
         at Microsoft.DotNet.MaestroConfiguration.Cli.ConfigurationValidator.ValidateConfiguration(ILocalGitRepo configurationRepo, String originalConfigurationBranch, String newConfigurationBranch) in /_/src/Microsoft.DotNet.MaestroConfiguration.Cli/ConfigurationValidator.cs:line 92

Example build: https://dev.azure.com/dnceng/internal/_build/results?buildId=2911815&view=logs&j=8f183919-ef98-5d4d-b21f-f2cc6adfe25f&t=613d5903-0643-55ed-f7e9-1d5cf836838f
From pull request: https://dev.azure.com/dnceng/internal/_git/maestro-configuration/pullrequest/58316

[adamzip]

As Premek wrote, it's expected that updating the batchable field on an existing subscription should fail at ingestion.

However, it should still be possible to delete and recreate a subscription with the new values for the immutable fields.

There's two things we should probably do:

• Currently, newly created subscriptions are compared against subs in the DB instead of subs in-memory. This is blocking the ability to update a subscription's immutable fields by changing its ID too. We should fix this
• In the darc update operation, we should detect if immutable fields are being updated, warn against it, and propose the option (e.g. with a y/n prompt) to create a PR that deletes and recreates the subscription with the updated values. We can also update the exception message on immutable field updates to propose this approach to the user.