Add IAC Gradle Plugin Suite

[ysb33r]

Describes the IAC Gradle plugin suite's support of OpenTofu

Motivation and Context

We have been integrating Terraform with Gradle for a number of years. Now we have finally got the time to properly support OpenTofu as well, with a feature set on par with what the Terraform plugins provide.

(If this change to supporters.json is inappropriate, jsut throw this PR away).

Types of changes

• [ ] Bug fix (non-breaking change which fixes an issue)
• [ ] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)
• [x] Docs update.

[ghost]

Hi @ysb33r thank you for your support. The right place to add this would be this file.

[ysb33r]

I'll fix it.