More options for `ambient new`

[philpax]

At present, ambient new generates a Playable without any fields filled in (authors, description). We should add options to specify these parameters and/or make it interactive, so that a user can specify what they want.

Options:

• name
• authors
• description
• content types, or for_playables
• public

and ambient_version should be automatically set.

[pierd]

Also something like ambient new --mod PACKAGE_ID/DEPLOYMENT_ID for creating mods.