Wires module update workflow for external repo callers.

[d-lazenby]

Summary

Wires the reusable Terraform module update workflow for external repository callers, adds contract validation, and expands consumer-facing documentation so downstream teams can adopt this tool reliably.

Context

No linked ticket. This branch (add-workflow-wiring) has been tested via a call from an external repository and is ready to merge.

Changes

• Rewrote update-tf-modules.yml to support cross-repo workflow_call with configurable inputs, outputs (changed, pr_number, pr_url), and PR flow controls
• Added contract validation workflow (test-reusable-workflow-contract.yml) that asserts output shape and enforces create_pr=false behaviour on each PR to main
• Expanded README with versioning policy, compatibility contract, token/permissions model, failure modes, troubleshooting guidance, and a minimal caller example
• Added manifest examples (example-manifest.yml, examples/update-modules-manifest.example.yml) as a quick-start reference for consumers
• Hardened runtime configuration handling in config.py to ensure the package install location is correct when called from a workflow

Testing

• Workflow invoked end-to-end from an external repository (https://github.com/datasciencecampus/test-update-tf-modules-workflow); PR was created successfully in the caller repo
• Contract validation workflow confirms changed is always true/false and that pr_number/pr_url are empty when create_pr=false
• Permissions troubleshooting path verified: explicit failure message and actionable guidance emitted when PR creation fails

Risks / Notes

• updater_ref defaults to add-workflow-wiring and should be updated to main (or a version tag) post-merge

Next steps

• Enrich the auto-generated update PR body with a concise run summary (changed file count, file list, workflow run link) reusing existing step outputs to avoid duplicated git diff logic
• Add ADR and finalise README to track most recent updates

[ColinDaglish]

Resolve conflicts, address code QL security alert comment, and add link to the repo you've tested this on.

[ColinDaglish]

Getting this error on the caller repo:

Failed to queue workflow run: Invalid Argument - failed to parse workflow: error parsing called workflow "" -> "datasciencecampus/update-tf-modules/.github/workflows/update-tf-modules.yml@add-workflow-wiring" (source branch with sha:e216094f54a89c9ac4846b7464d72fb1db39a118) : (Line: 177, Col: 9): 'uses' is already defined

[ColinDaglish]

Looking really good. On the whole I think this is nearly there.

Required

• Fix versions to commit SHA's for mutability
• Need to see working example

Optional

• Consider hard coding values which won't change (e.g updater_repository)
• Consider splitting readme into single purpose driven docs (contributing guidance, variable reference guide, etc).

[ColinDaglish]

Nice work!