ci: skip Konflux builds and e2e for docs-only PRs (#634)

## Summary
- Add CEL path filter to `.tekton/` PipelineRun definitions so that PRs
touching only `docs/**` or `**/*.md` files skip the Konflux multi-arch
container builds and downstream e2e integration tests
- Document the full CI landscape (Konflux pipelines, integration tests,
GitHub Actions) in CONTRIBUTING.md

## Motivation
Previously, a docs-only PR triggered 8 container image builds (2
components x 4 architectures) and an e2e test suite that provisions an
ephemeral OpenShift cluster on AWS. None of these are meaningful for
documentation changes.

## Changes
- `.tekton/odh-maas-api-pull-request.yaml` — added `!files.all.all(x,
x.matches('^docs/') || x.matches('\.md$'))` to the CEL expression
- `.tekton/odh-maas-controller-pull-request.yaml` — same CEL filter
- `CONTRIBUTING.md` — added Konflux/Tekton pipelines section,
integration tests documentation, GitHub Actions summary table, and
docs-only skip explanation

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->
## Summary by CodeRabbit

* **Chores**
* Adjusted PR pipeline triggers to skip Konflux/Tekton runs for
docs-only changes, reducing unnecessary CI executions.

* **Documentation**
* Revised contributing guide to describe the two-system CI model (GitHub
Actions and Konflux/Tekton), responsibilities, multi-architecture image
builds, PR vs main trigger behavior, and Konflux-driven integration
smoke tests.
<!-- end of auto-generated comment: release notes by coderabbit.ai -->

Author: mynhardtburger

.tekton/odh-maas-api-pull-request.yaml

@@ -9,7 +9,7 @@ metadata:
     pipelinesascode.tekton.dev/cancel-in-progress: "false"
     pipelinesascode.tekton.dev/max-keep-runs: "3"
     pipelinesascode.tekton.dev/on-cel-expression: event == "pull_request" && target_branch
-      == "main"
+      == "main" && !files.all.all(x, x.matches('^docs/') || x.matches('\\.md$'))
   creationTimestamp: null
   labels:
     appstudio.openshift.io/application: opendatahub-builds

.tekton/odh-maas-controller-pull-request.yaml

@@ -9,7 +9,7 @@ metadata:
     pipelinesascode.tekton.dev/cancel-in-progress: "false"
     pipelinesascode.tekton.dev/max-keep-runs: "3"
     pipelinesascode.tekton.dev/on-cel-expression: event == "pull_request" && target_branch
-      == "main"
+      == "main" && !files.all.all(x, x.matches('^docs/') || x.matches('\\.md$'))
   creationTimestamp: null
   labels:
     appstudio.openshift.io/application: opendatahub-builds

CONTRIBUTING.md

@@ -61,10 +61,37 @@ This project follows a **Stream-Lake-Ocean** release model. Code flows from acti
 | `maas-controller/` | Kubernetes controller for MaaS CRDs; see [maas-controller/README.md](maas-controller/README.md) |
 | `docs/` | User and admin documentation (MkDocs); [online docs](https://opendatahub-io.github.io/models-as-a-service/) |
 | `test/` | E2E and billing/smoke tests |
-| `.github/workflows/` | CI (build, PR title validation, MaaS API lint/build) |
+| `.github/workflows/` | GitHub Actions CI (lint, build, PR title validation, docs) |
+| `.tekton/` | Konflux/Tekton pipeline definitions for container image builds |
 
 ## CI and checks
 
+This project uses two CI systems: **Konflux** (Tekton-based) for container image builds and integration testing, and **GitHub Actions** for linting, unit tests, and documentation.
+
+### Konflux / Tekton pipelines
+
+Konflux builds multi-arch container images (x86_64, arm64, ppc64le, s390x) for both `maas-api` and `maas-controller` on every PR and push to `main`. Pipeline definitions live in `.tekton/` and reference a shared pipeline from [odh-konflux-central](https://github.com/opendatahub-io/odh-konflux-central) (`pipeline/multi-arch-container-build.yaml`).
+
+| Pipeline | Trigger | Output image |
+|----------|---------|--------------|
+| `odh-maas-api-on-pull-request` | PR to `main` | `quay.io/opendatahub/maas-api:odh-pr` |
+| `odh-maas-api-on-push` | Push to `main` | `quay.io/opendatahub/maas-api:odh-stable` |
+| `odh-maas-controller-on-pull-request` | PR to `main` | `quay.io/opendatahub/maas-controller:odh-pr` |
+| `odh-maas-controller-on-push` | Push to `main` | `quay.io/opendatahub/maas-controller:odh-stable` |
+
+**Integration tests (e2e):** When a PR build completes, Konflux runs an integration test that provisions an ephemeral OpenShift cluster (HyperShift on AWS), deploys the ODH stack with the newly built images, and runs `test/e2e/scripts/prow_run_smoke_test.sh`. This is defined in `odh-konflux-central` under `integration-tests/models-as-a-service/`.
+
+**Docs-only skip:** PRs that only touch documentation files (`docs/**` or `**/*.md`) skip the Konflux build pipelines and integration tests entirely. This is controlled via a CEL expression in the `.tekton/` pipeline definitions.
+
+### GitHub Actions
+
+| Workflow | Trigger | Path filter | What it checks |
+|----------|---------|-------------|----------------|
+| PR Title Validation | Every PR | None | Semantic PR title format (`type: subject`) |
+| MaaS API | PR + push to `main` | `maas-api/**` (PR only) | golangci-lint, unit tests, image build |
+| Build | PR + push to `main` | `maas-controller/api/**`, `deployment/**`, etc. (PR only) | Kustomize manifest validation, CRD codegen verification |
+| Docs | PR + push to `main` | `docs/**`, `**/*.md` | Link validation, mkdocs build, GitHub Pages deploy |
+
 - **PR title:** Must follow semantic format (`type: subject`, subject not starting with a capital). Use `draft`/`wip` label to bypass.
 - **Kustomize:** Manifests under `deployment/` are validated with `scripts/ci/validate-manifests.sh` (kustomize build).
 - **MaaS Controller codegen:** CI verifies that generated deepcopy code (`maas-controller/api/maas/v1alpha1/zz_generated.deepcopy.go`) and CRD manifests (`deployment/base/maas-controller/crd/bases/`) are in sync with the API types. If you change any file under `maas-controller/api/`, run `make -C maas-controller generate manifests` and commit the results before pushing. The check fails when uncommitted generated changes are detected.