[Feature]: adopt terraform protocol v6

[ctreatma]

Description

Currently this provider uses terraform protocol v5. This prevents us from using some nicer features of terraform-plugin-framework, especially around nested schemas.

The impact of moving from terraform protocol v5 to v6 should largely be internal to the provider, but it does mean dropping support for terraform <1 and should be done in a major release unless we can effectively demonstrate that this provider is not actively used with terraform <1.

New or Affected Terraform Resources

No response

Potential Terraform Configuration

No response