.tekton/pull-request: re-format CEL expression

Also add comments.

Signed-off-by: Adam Cmiel <[email protected]>

.tekton/pull-request.yaml

@@ -4,7 +4,15 @@ kind: PipelineRun
 metadata:
   name: build-definitions-pull-request
   annotations:
-    pipelinesascode.tekton.dev/on-cel-expression: (event == "pull_request" && target_branch == "main" && ( !has(body.pull_request) || !body.pull_request.draft) ) || (event == "push" && target_branch.startsWith("gh-readonly-queue/main/"))
+    pipelinesascode.tekton.dev/on-cel-expression: |
+      (
+          // PR to "main" branch, not draft
+          event == "pull_request" && target_branch == "main"
+          && (!has(body.pull_request) || !body.pull_request.draft)
+      ) || (
+          // PR enters the merge queue
+          event == "push" && target_branch.startsWith("gh-readonly-queue/main/")
+      )
     pipelinesascode.tekton.dev/task: "[task/git-clone/0.1/git-clone.yaml, .tekton/tasks/buildah.yaml, .tekton/tasks/yaml-lint.yaml, .tekton/tasks/e2e-test.yaml, task/sast-snyk-check/0.1/sast-snyk-check.yaml]"
     pipelinesascode.tekton.dev/task-2: "yaml-lint"
     pipelinesascode.tekton.dev/max-keep-runs: "5"