Add support for organization resources, provisioners and org, group, role sync

[ethanndickson]

This allows users to create and manage multi-org Coder deployments using Terraform.
Although the organization API hasn't been finalised/released, we can implement an initial version of this.
The resource should allow users to create and assign custom organization-wide roles.

• org operations
• provisioner keys
• group/role sync

nice-to-have

• org sync

[bpmct]

Also group, org, role sync

[ethanndickson]

Worth mentioning that the tests for this should use the new statecheck package - it feels a lot more ergonomic, though I don't think there's a need to port the existing tests over.

Example: hashicorp/terraform-provider-random#599

[bpmct]

@aslilac is this completed by #131?

[aslilac]

that's just one piece of the puzzle. I've got at least one more PR to merge to make a certain customer happy, and there are a couple more pieces after that even.