feat: allow backend role arn to init (AIR-1495)

[glaracuente]

what

• Allow a backend role arn to be used during init

why

• We've had interest in using a backend role for local tf operations, as an alternative to defining an assume_role within backend config or relying on ambient credentials.

references

• AIR-1495

Summary by CodeRabbit

• New Features
  • Backend role ARN configuration is now supported through environment variables during initialization, providing greater flexibility for infrastructure deployments. This enhancement streamlines multi-environment setup workflows and eliminates the need for code modifications when managing backend configurations.

[gberenice]

@glaracuente is it intended to be in thedraft state?

[glaracuente]

@glaracuente is it intended to be in thedraft state?
This one wasn't supposed to be, thanks. I've marked as ready.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Pro

Run ID: f310ea81-8db4-46e5-9a1d-e1c91f81e823

📥 Commits

Reviewing files that changed from the base of the PR and between 953d140 and f2dde09.

📒 Files selected for processing (1)

• lib/tf/Taskfile.yml

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📝 Walkthrough

Walkthrough

This change modifies the Terraform/OpenTofu init task in lib/tf/Taskfile.yml to support configuring the backend role ARN. It introduces a new task-level variable TF_BACKEND_ROLE_ARN sourced from the environment and updates the init command to conditionally append -backend-config="role_arn=..." when the variable is set, otherwise executing the standard init with only {{.TF_ARGS}}.

Estimated code review effort

🎯 1 (Trivial) | ⏱️ ~3 minutes

Possibly related PRs

• feat(tf): update the tf:init command to work for TF dynamic backends #40 — Also modifies the tf:init task's backend-config handling; that PR removed explicit backend-config usage to support dynamic backends, while this PR adds conditional role_arn backend-config support.

Suggested reviewers

• gberenice
• Gowiem

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title directly relates to the main change: introducing support for configuring backend role ARN in the Terraform init task.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feature/AIR-1495/optional_backend_role_arn

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