Gesture to generate parameter placeholders for CI/CD

When trying to onboard an Aspire app to a CI/CD pipeline, you need to know all the required "inputs". For example, if deploying to Azure, at a minimum you need:

* `Azure__TenantId`
* `Azure__SubscriptionId`
* `Azure__ResourceGroup`

and optionally:

* `Azure__Location`
* `Azure__AllowResourceGroupCreation`

Then also, for every Parameter in the AppHost, you need to supply a value.

We should make some gesture that tells a user which inputs - specifically in the correct format, like environment variable names - they will need to supply to make an `aspire deploy --non-interactive` call to work in their CI/CD pipeline.