[ENH] - Option to set a custom name for an app

[pmeier]

Feature description

Add an option to set a custom name for a deployed app instead of assigning it a random ID. If the name is already used by a different app, the form should display an error.

Value and/or benefit

1. Apps that are deployed (semi-)permanently could have a human digestible and memorable URL.
2. Apps that need to know the path prefix before they are deployed, e.g. FastAPI, can be deployed in a single step. Right now, the only way to do this is to deploy once, which will fail as expected. At that point the prefix is known and we can restart the app and supplying the prefix.

Anything else?

Talked with @aktech about this offline.