fix(resource/github_organization_custom_properties): allow for import

[pippitt]

Implemented import functionality on resourcegithub_organization_custom_properties
renamed file to match others (s to z)
add some testing

Resolves #2828

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Before the change?

• Could not import the organization_custom_properties resource
  local example

$ terraform import github_organization_custom_properties.point_of_contact Point-of-Contact
Acquiring state lock. This may take a few moments...
github_organization_custom_properties.point_of_contact: Importing from ID "Point-of-Contact"...
github_organization_custom_properties.point_of_contact: Import prepared!
  Prepared github_organization_custom_properties for import
github_organization_custom_properties.point_of_contact: Refreshing state... [id=Point-of-Contact]
╷
│ Error: GET https://api.github.com/orgs/missionlane/properties/schema/: 404 Not Found []
│
│
╵

Releasing state lock. This may take a few moments...

After the change?

• Can import organization_custom_properties resource
  local example from updated

$ terraform import github_organization_custom_properties.point_of_contact Point-of-Contact
Acquiring state lock. This may take a few moments...
github_organization_custom_properties.point_of_contact: Importing from ID "Point-of-Contact"...
github_organization_custom_properties.point_of_contact: Import prepared!
  Prepared github_organization_custom_properties for import
github_organization_custom_properties.point_of_contact: Refreshing state... [id=Point-of-Contact]

Import successful!

The resources that were imported are shown above. These resources are now in
your Terraform state and will henceforth be managed by Terraform.

Pull request checklist

• Schema migrations have been created if needed (example) - not needed
• Tests for the changes have been added (for bug fixes / features)
• Docs have been reviewed and added / updated if needed (for bug fixes / features) -current docs have correct import

Does this introduce a breaking change?

Please see our docs on breaking changes to help!

• Yes
• No

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[pippitt]

borrowed from existing tests, working on the linting error

[nickfloyd]

❤️