feat: add opentofu plugin

[virtualroot]

Summary

Description:

• Tool repo URL: https://github.com/opentofu/opentofu
• Plugin repo URL: https://github.com/virtualroot/asdf-opentofu

Checklist

• Format with scripts/format.bash
• Test locally with scripts/test_plugin.bash --file plugins/<your_new_plugin_name>
• Your plugin CI tests are green
  • Tip: use the plugin_test action from asdf-actions in your plugin CI

[virtualroot]

Hey @jthegedus 👋

I noticed there are a couple of new PRs for this same tool.

I want to ask to please consider merging this one rather than the alternatives since this one was announced and has been in use by the OpenTofu community since the first alpha release.

I want to avoid confusion for the many users already using it.