Extract the rest of the Models to Model module

[adamjcampbell]

Provides more separation for our domain models for moving to a more modular architecture

📝 Summary of Changes

Changes proposed in this pull request:

• Moves the rest of the Models in AppStoreConnectCLI to Model

⚠️ Items of Note

We lose the auto generated struct initialiser because it isn't public so we have to manually write it. Also I have not redefined the SDK enums so many things that were previously stored as enum are now String by passing their rawValue

[adamjcampbell]

@Nafisa2020 The end goal is to move the SDK to a Network module so a lot of the imports will disappear as a result. There will be no conflicting imports at the Command level, which will be nice

You're right, it's a little messy but it should tidy up as we progress