Add stacks plugin proto

[Uk1288]

Fixes #

• This PR implements the subcommand terraform stacks
• The new command terraform stacks exposes some Terraform Stack operations through the cli. The available subcommands depend on the stacks plugin implementation.

NOTE: the terraform stacks -help will be implemented in a separate PR

Target Release

1.13.x

CHANGELOG entry

• The new command terraform stacks exposes some Terraform Stack operations through the cli. The available subcommands depend on the stacks plugin implementation. Use terraform stacks -help to see available commands.

• This change is user-facing and I added a changelog entry.

• This change is not user-facing.

NOTE: Test steps are written in the project slack channel

[github-actions]

Changelog Warning

Currently this PR would target a v1.13 release. Please add a changelog entry for in the .changes/v1.13 folder, or discuss which release you'd like to target with your reviewer. If you believe this change does not need a changelog entry, please add the 'no-changelog-needed' label.