Enable Importer Functionality for Resources

[wtran63]

Currently terraform import is not supported on all resources. This feature would allow greater flexibility for those that are moving from an unmanaged to a terraform managed keboola instance.

https://www.terraform.io/docs/extend/resources.html#importers

[wtran63]

Double checking the code, the importer is available for most resources except a few:

• Extractors
• Storage Table
• Writer Tables

With regard to Storage tables: Because the resource forces the user to destroy and recreate a resource anyways after import, there's no reason to be able to import, other than having terraform take over managing that specific ID

• I have not double checked extractors and writer tables.