Reuse CI workflows to build downstream dependencies

[john-h-kastner-aws]

Category

Internal refactors/changes

Describe the feature you'd like to request

The CI workflow used by this repository to build the downstream dependencies in cedar-spec, cedar-examples, and cedar-java duplicates the workflows found in those individual repositories. We should reuse these workflows so that CI doesn't break when a change made in a downstream repository isn't copied here.

Relevant workflows:

• cedar-examples: https://github.com/cedar-policy/cedar-examples/blob/main/.github/workflows/ci.yml
• cedar-java: https://github.com/cedar-policy/cedar-java/blob/main/.github/workflows/ci.yml
• cedar-spec: https://github.com/cedar-policy/cedar-spec/blob/main/.github/workflows/ci.yml

Describe alternatives you've considered

.

Additional context

No response

Is this something that you'd be interested in working on?

• 👋 I may be able to implement this feature request
• ⚠️ This feature might incur a breaking change

[andrewmwells-amazon]

• tinytodo
• cedar-rust-hello-world
• cedar-example-use-cases
• cedar-java
• cedar-spec

[john-h-kastner-aws]

The current reusable downstream builds turn out not to work for PRs coming from forks. See this failed workflow: https://github.com/cedar-policy/cedar/actions/runs/7451426259/job/20272524590

[john-h-kastner-aws]

Fork build failure was fixed by cedar-policy/cedar-examples#90. We need to depended on a rev instead of a branch to correctly find the PR branch across forks. We then have to refer to our main branch as refs/heads/main