ci: inject gfx-ci/linux S3 artifacts without rebuilding containers

We need update kernel often. We need test kernel changes often.

Introduced `KERNEL_EXTERNAL_TAG` to differ between `KERNEL_TAG` which is
also used to rebuild the containers. We don't need rebuild containers
for the external kernel, so this way we don't have to.

Updating kernel goes wruuuuuum.

Signed-off-by: David Heidelberg <david.heidelberg@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/23563>

.gitlab-ci.yml

@@ -6,20 +6,29 @@ workflow:
     # merge pipeline
     - if: $GITLAB_USER_LOGIN == "marge-bot" && $CI_COMMIT_BRANCH == null
       variables:
+        KERNEL_IMAGE_BASE: https://${S3_HOST}/mesa-lava/${KERNEL_REPO}/${KERNEL_TAG}
         MESA_CI_PERFORMANCE_ENABLED: 1
         VALVE_INFRA_VANGOGH_JOB_PRIORITY: ""  # Empty tags are ignored by gitlab
     # post-merge pipeline
     - if: $GITLAB_USER_LOGIN == "marge-bot" && $CI_COMMIT_BRANCH
       variables:
+        KERNEL_IMAGE_BASE: https://${S3_HOST}/mesa-lava/${KERNEL_REPO}/${KERNEL_TAG}
         JOB_PRIORITY: 40
         VALVE_INFRA_VANGOGH_JOB_PRIORITY: priority:low
     # any other pipeline
-    - if: $GITLAB_USER_LOGIN != "marge-bot"
+    - if: $GITLAB_USER_LOGIN != "marge-bot" && $FORCE_KERNEL_TAG != null
       variables:
+        KERNEL_IMAGE_BASE: https://${S3_HOST}/mesa-lava/${KERNEL_REPO}/${FORCE_KERNEL_TAG}
+        JOB_PRIORITY: 50
+        VALVE_INFRA_VANGOGH_JOB_PRIORITY: priority:low
+    - if: $GITLAB_USER_LOGIN != "marge-bot" && $FORCE_KERNEL_TAG == null
+      variables:
+        KERNEL_IMAGE_BASE: https://${S3_HOST}/mesa-lava/${KERNEL_REPO}/${KERNEL_TAG}
         JOB_PRIORITY: 50
         VALVE_INFRA_VANGOGH_JOB_PRIORITY: priority:low
     - when: always
 
+
 variables:
   FDO_UPSTREAM_REPO: mesa/mesa
   MESA_TEMPLATES_COMMIT: &ci-templates-commit d5aa3941aa03c2f716595116354fb81eb8012acb
@@ -35,7 +44,6 @@ variables:
   PIPELINE_ARTIFACTS_BASE: ${S3_HOST}/artifacts/${CI_PROJECT_PATH}/${CI_PIPELINE_ID}
   # per-job artifact storage on MinIO
   JOB_ARTIFACTS_BASE: ${PIPELINE_ARTIFACTS_BASE}/${CI_JOB_ID}
-  KERNEL_IMAGE_BASE: https://${S3_HOST}/mesa-lava/gfx-ci/linux/${KERNEL_TAG}
   # reference images stored for traces
   PIGLIT_REPLAY_REFERENCE_IMAGES_BASE: "${S3_HOST}/mesa-tracie-results/$FDO_UPSTREAM_REPO"
   # For individual CI farm status see .ci-farms folder