Importer Improvements

[duncanmcclean]

This pull request makes various changes around the importer commands. Changes include but are not limited to:

• Changed the console output, to improve styling.
• Tweaked some of the language around command descriptions and argument descriptions.
• Added tests to cover all of the importer commands
  • No tests existed for the importers until now. I had spotted a few errors in my manual testing so I was able to squash them by writing tests.
• Fixed an issue when import form submissions
  • It was still trying to use the ->submissions() relationship on the Form model, which was removed in Split forms and form submissions, provide Eloquent Submission Repository and Query Builder #177.
  • I've changed it to instead create directly on the configured Submission model.
• Fixed an error when importing asset containers
  • When the previous importer code was calling ->toModel(), it was touching was a core AssetContainer class which didn't have a toModel class on it, causing it to be sent through the augmentation stuff and error out.
  • I've added a new makeModelFromContract method to the AssetContainer class, which seems to be how the new importer implementations work.
• Refactored the guards around determining which stuff should be imported, by introducing new shouldImport... methods.
• Added --only-* arguments to some importers responsible for importing multiple things
  • These new arguments allow for doing --only-assets or --only-form-submission on importer commands which can import multiple things like importing asset containers & assets or forms & form submissions.

This PR started out small but grew arms and legs once I decided to add tests for everything 😆 .

Related: statamic/cms#9669.

To Do

• Fix failing tests in ImportGlobalsTest
• Add tests for all the importer commands
• Fix failing tests in ImportEntriesTest
  • The tests seem to be importing entries with their old Stache ID, which is a string. However, the database migration is expecting an integer, causing it to fail. Setting the $shouldUseStringEntryIds property doesn't seem to help.
• Fix issue with the collection importer when entries are in the Stache
  • Target class [statamic.eloquent.entries.model] does not exist.