docs: link source field to AWS S3 access operator notes

[deepak0x]

Issue

coreos/butane#662 — the source field docs list s3/arn as supported schemes but are silent on how S3 credentials are resolved at runtime.

Approach

As agreed with @pabo99 / @prestist in the issue thread, the fix belongs upstream in Ignition's config/doc/ignition.yaml (Butane's spec docs are generated from this file, and the butane and ignition repos are now merged). The source field description now links to Ignition's AWS S3 access operator notes, which document the supported s3:///arn:... URL formats and credential resolution.

This follows the existing pattern used by other fields that link to operator-notes/#... (e.g. the filesystem wipe descriptions).

Verification

• config/doc/ignition.yaml and butane/internal/doc/butane.yaml parse as valid YAML.
• The openshift variant's source transform (a full-replacement regex ending at "haven't been modified.") is unaffected — it still replaces the whole description with "Only the data scheme is supported." for openshift, which remains correct.

Fixes coreos/butane#662

[coderabbitai]

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ℹ️ Recent review info

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📥 Commits

Reviewing files that changed from the base of the PR and between 3ec5322 and 21732a0.

📒 Files selected for processing (1)

• config/doc/ignition.yaml

📜 Recent review details

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📓 Path-based instructions (1)

config/**

⚙️ CodeRabbit configuration file

config/**: The config/ directory is the frontend stable library API consumed by external programs (e.g., Butane). API-breaking changes require bumping the Ignition major version. Ensure backward compatibility.

Files:

• config/doc/ignition.yaml

🔇 Additional comments (1)

config/doc/ignition.yaml (1)

4-4: LGTM!

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📝 Walkthrough

Walkthrough

The resource source description now documents supported AWS S3 and ARN URL formats and links to Ignition’s AWS S3 access documentation.

Changes

Source URL documentation

Layer / File(s)	Summary
Document AWS S3 source formats config/doc/ignition.yaml	The source URL description now includes AWS S3 and ARN access formats with a link to AWS S3 access guidance.

Estimated code review effort: 1 (Trivial) | ~2 minutes

Merge Risk: ⚪ Minimal · up to 21732

This localized documentation update adds the missing AWS S3 credential-resolution reference without changing runtime behavior; no actionable merge-blocking risk remains after normal checks and review.

🚥 Pre-merge checks | ✅ 6

✅ Passed checks (6 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title uses the required subsystem prefix, starts with a lowercase imperative description, and accurately summarizes the documentation change.
Description check	✅ Passed	The description clearly explains the AWS S3 documentation update, its rationale, implementation, verification, and linked issue.
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.
Commit Message Convention	✅ Passed	The PR has one non-merge commit: docs: link source field to AWS S3 access operator notes; docs is a valid subsystem, and link is lowercase imperative with no trailing period.

✨ Finishing Touches

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• Create PR with unit tests

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[deepak0x]

Closing in favor of #2251, which does the same thing but correctly.

Both PRs add the pointer to the AWS S3 access operator notes in config/doc/ignition.yaml. The difference is what ships to the docs site:

• docs: link source field to S3 access operator notes #2251 regenerates the committed docs/configuration-v3_*.md files, so the link actually shows up in the rendered spec. I confirmed regenerated output matches the committed files (0 diffs).
• This PR only touches ignition.yaml and leaves the generated docs stale (8 files out of sync). The site serves the generated md files, not the schema source, so the fix would never render until someone regenerates.

Keeping the one that lands the change end to end. Thanks for the quick review on the earlier version.