Conditional content for certain deployments

[dahlsailrunner]

Consider the following lines from an AppHost:

var postgesdb = builder.AddPostgres("postgres")
                          .AddDatabase("mydatabase");

var emailService = builder.AddSmtp4Dev("smtp-4-dev")  // custom extension
    .WithExternalHttpEndpoints();

These add a Postgres database and the rnwood/smtp4dev container image (it's like MailDev).

When I deploy this to Azure Container Apps for an initial testing environment, it would be great to leave it exactly as it is. But for higher environments, and certainly production, I would be using an Azure Postgres Flexible Server, and an actual email service like SendGrid.

I've seen the syntax for builder.ExecutionContext.IsPublishMode and could use that for ALL deployments, but I'm wondering if there is guidance or thoughts on how to do this differently for certain deployments.

Maybe different appSettings.<env>.json values for a setting like useAzureFlexiblePostgres and useRealEmailService?
Is there a way to determine in publish mode what environment is being used for azd up?

The best / cleanest thing I've come up with so far is to simply use azd up for the early testing deployments, and then for higher environments and production to build my own containers with dotnet publish and deploy them with the appropriate configuration using traditional means.

I've also seen this API proposal for When() that might do a good job at this, too.
#5192

Appreciate any thoughts. :)