feat(gitcommit): add Git commit source resource - #9609

Fix #2052

Add a gitcommit resource. The source returns the latest commit hash for a Git branch; the condition checks that a commit exists in a repository. Both support repository URLs, local paths, and SCM working directories. Branch lookup resolves local and origin refs without checking out the branch or modifying the working tree.

The condition hash defaults to the source output and can be overridden with spec.hash; abbreviated hashes are resolved with the Git revision syntax.

The resource is registered in the pipeline mapping and includes an end-to-end manifest covering URL, path, and SCM inputs plus two condition scenarios.

Test

go test ./pkg/plugins/resources/gitcommit -count=1
go test ./pkg/plugins/utils/gitgeneric -run '^TestGetCommitHash$|^TestIsCommitExist$' -count=1
go test ./pkg/core/pipeline/resource -count=1
go vet ./pkg/plugins/resources/gitcommit ./pkg/plugins/utils/gitgeneric ./pkg/core/pipeline/resource

Additional Information

Checklist

• Documentation companion: updatecli/website#3563

Tradeoff

The target stage returns an explicit unsupported error because a commit hash is immutable. The condition checks commit existence, defaulting to the source output with spec.hash as an override.

Potential improvement

A future changelog implementation could expose commits between two source revisions.