Create dynamic defaults for service creation

[brmzkw]

The command koyeb service create myservice --app myapp creates a default port (80:http) and route (/:80).

If the port is overriden but not the route, the default route is still created and the service creation will fail:

$> koyeb service create myservice --app test --docker nginx --port 9999
❌ Error while creating the service: the Koyeb API returned an error 400: Validation error

🔎 Additional details
Field definition.routes.0.port: unknown port "80"

🏥 How to solve the issue?
Fix the request, and try again

🕦 The original error was:
400 Bad Request

To solve the issue, the route must also be overridden:

koyeb service create myservice --app test --docker nginx --port 9999 --route /:9999
INFO[0000] Service deployment in progress. Access deployment logs running: koyeb service logs fe91a7cd.

If only one of the route or the port is set, we should use it's value to compute the other flag's default.