chore: replace deprecated type schema.ImportStatePassthrough

[tenthirtyam]

Summary of Pull Request

The type schema.ImportStatePassthrough has been deprecated in favour of schema.ImportStatePassthroughContext in the SDK helper/schema.

References:

• https://www.terraform.io/docs/extend/guides/v2-upgrade-guide.html#more-support-for-context-context
• Context aware SDK with timeouts hashicorp/terraform-plugin-sdk#276

Type of Pull Request

• This is a bug fix.
• This is an enhancement or feature.
• This is a code style/formatting update.
• This is a documentation update.
• This is a refactoring update.
• This is a chore update
• This is something else.
  Please describe:

Related to Existing Issues

Test and Documentation Coverage

For bug fixes or features:

• Tests have been completed.
• Documentation has been added/updated.

Breaking Changes?

• Yes, there are breaking changes.
• No, there are no breaking changes.

[salv-orlando]

As we have a large feature branch that needs to be merged back in master, it might be worth applying commit like this once we merge the feature branch - and of course implementing the same changes there too.