Add Tekton tasks, pipeline and test Dockerfile

- Add git-clone task for repository cloning
- Add kaniko-build task for container image builds
- Add container-build pipeline orchestrating clone + build
- Add harbor-credentials ExternalSecret for innoventions namespace
- Add test-app.Dockerfile for pipeline validation

Day 3 deliverables for Tekton Phase 2

test-app.Dockerfile

@@ -0,0 +1,6 @@
+FROM alpine:3.21
+RUN apk add --no-cache curl
+LABEL org.opencontainers.image.source="https://gitea.mk-labs.cloud/rblundon/homelab"
+LABEL org.opencontainers.image.description="Test application for Tekton pipeline validation"
+LABEL org.opencontainers.image.title="tekton-test-app"
+CMD ["echo", "Hello from Tekton Pipeline! Build successful."]