Add content type schema unarchive option

[philipbushnell-valtech]

It appears the provider doesn't unarchive a schema if it's added back to the terraform.

The provider fails with the following error:

This occurs after the following steps:

• Add a schema (CREATE)
• Apply
• Destroy the schema (ARCHIVE)
• Apply
• Re-add the same schema (UNARCHIVE)
• Apply

@pimvernooij has suggested to raise this as the functionality has apparently not been implemented yet.