CI: capture stdout/stderr output to artifact files (#24401)

Gitlab truncates job trace output (even the complete raw output) at 4MB,
so this change captures it to a file under "user_data" artifacts as well,
to make sure we can debug output from the end of the rebuild job.

share/spack/gitlab/cloud_pipelines/stacks/e4s/spack.yaml

@@ -327,7 +327,8 @@ spack:
       - cd ${SPACK_CONCRETE_ENV_DIR}
       - spack env activate --without-view .
       - spack config add "config:install_tree:projections:${SPACK_JOB_SPEC_PKG_NAME}:'morepadding/{architecture}/{compiler.name}-{compiler.version}/{name}-{version}-{hash}'"
-      - spack -d ci rebuild
+      - mkdir -p ${SPACK_ARTIFACTS_ROOT}/user_data
+      - spack -d ci rebuild > >(tee ${SPACK_ARTIFACTS_ROOT}/user_data/pipeline_out.txt) 2> >(tee ${SPACK_ARTIFACTS_ROOT}/user_data/pipeline_err.txt >&2)
 
     mappings:
       - match: