Add possibility to swap stopped Azure Functions and slots.

[fsmartini]

We have been using deployment slots for a while now, but we have one major issue with them: both the production slot and the deployment slot must be running to allow a swap. This is quite inconvenient for us, because we often use Service Bus triggers and do not want the apps to start processing messages until we are certain that all apps in the chain have been deployed with the new code and swapped in.

Ideally, we would like to have the ability to keep them turned off during the swap process, allowing us to start the production slot only after the pipelines confirm that the swap is complete.

Is there an architectural reason it works this way today, or is it simply due to the typical use case for slots, where code is expected to go live seamlessly?

And of course, if our understanding of how to use these are wrong, please help us getting the hang of it.

Best regards, Fredrik