[Issue] Enable azure.yaml to specify optional deployments for services

[pamelafox]

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Our situation: we have an appservice host, and if the user sets a current azd variable, we also want to deploy a functionapp for an additional microservice.

We discussed this in an internal teams thread here: https://teams.microsoft.com/l/message/19:[email protected]/1708030654691?tenantId=72f988bf-86f1-41af-91ab-2d7cd011db47&groupId=c99e8504-1250-4d95-a824-9778e0e626c7&parentMessageId=1708030654691&teamName=Azure%20Developer%20CLI%20(azd)%20Partners&channelName=General&createdTime=1708030654691

Here's a syntax that Victor suggested:

That would work perfectly for our use case.

And he even suggested that we could switch the platform (like to change between AppService and ACA):

Without this feature, I think we will end up having to use the Azure CLI for the deployment, or forcing developers to un-comment, which is quite inelegant and prone to error.

Thanks!