lint-ci-config: Generate jobs-metadata.json

We also now save the jobs-metadata.json and jobs.yaml file as artifacts
as:

* It might be useful for someone who is modifying CI to copy jobs.yaml
  if they are having trouble regenerating locally.
* jobs-metadata.json is very useful for downstream pipelines to work out
  the right job to download.

Fixes #23654

.gitlab-ci.yml

@@ -278,6 +278,13 @@ lint-ci-config:
     - nix run .gitlab/generate-ci#generate-jobs
     # 1 if .gitlab/generate_jobs changed the output of the generated config
     - nix shell nixpkgs#git -c git diff --exit-code
+    # And run this to generate the .gitlab/jobs-metadata.json
+    - nix run .gitlab/generate-ci#generate-job-metadata
+  artifacts:
+    when: always
+    paths:
+      - .gitlab/jobs-metadata.json
+      - .gitlab/jobs.yaml
   dependencies: []
 
 lint-submods: