Allow to specify the application name/service name in koyeb app init

[brmzkw]

The command koyeb app init creates an application and a service. For example koyeb app init myapp --docker nginx --port 80 creates an app named myapp, and a service with the same name.

It is not possible to specify a custom application name.

We should allow the syntax app_name/service_name, and also to specify --app and --service.

[hanshal101]

Hey @brmzkw I would like to work on this issue.

[brmzkw]

Of course!