feat: support setting navigationItem for page in create-app-definition [EXT-5884]

[whitelisab]

When creating an app definition and having the page location selected, you can pass an optional navigationItem property which determines whether the page app should appear in the apps dropdown menu and what the name and path for that link should be. This is supported in the Contentful web app when creating and editing an app definition, but it is not supported in our Create App Definition script as part of the @contentful/app-scripts package. This PR adds this functionality to this script.

I have tested this locally and can confirm that the prompts appear correctly when the page location is selected and that the validations provide warnings correctly. The validations for the link name and path are using the same validations on the input fields in the web app.

Here is the experience in the web app:

Here is what the new prompts look like when using the Create App Definition script: