Improve documentation of how the executable name is determined

### What is the problem or limitation you are having?

Command line apps are primarily invoked by name from a terminal. However, briefcase doesn't currently allow specifying a name for just the executable, forcing us to specify it as the app's formal name. It might be desirable to make the two distinct so that the formal name can be relegated to branding and/or to be used in an installer while the executable can be spelled/capitalized differently.

### Describe the solution you'd like

My proposal is to allow `console_app` to contain a string value: the executable name. This way, it can be configured while also marking an app as a console app, using only one setting in the process. This way, the old behavior can also be kept, meaning the formal name can simply be used as usual if `console_app` is set to true instead of a string.

### Describe alternatives you've considered

There are no real alternatives besides tolerating this limitation.

### Additional context

_No response_