CHORE: Remove Tekton CI/CD platform

- Delete tekton/ directory (pipeline, triggers, dashboard, ci-cd)
- Remove tekton references from kustomization.yaml
- Switching to GitHub Actions for CI/CD

tekton/ci-cd/manifests/triggers/triggerbinding.yaml

@@ -1,17 +0,0 @@
-apiVersion: triggers.tekton.dev/v1beta1
-kind: TriggerBinding
-metadata:
-  name: github-push-binding
-  namespace: tekton-pipelines
-spec:
-  params:
-    - name: git-url
-      value: $(body.repository.clone_url)
-    - name: git-revision
-      value: $(body.after)
-    - name: git-branch
-      value: $(extensions.branch_name)
-    - name: repo-name
-      value: $(body.repository.name)
-    - name: repo-full-name
-      value: $(body.repository.full_name)