Trigger Shotgun pipelines using multi-project pipeline mechanism

In theory this change should be no-op, but in practice it is a
workaround for https://gitlab.com/gitlab-org/gitlab/-/issues/355590

.gitlab-ci.yml

@@ -346,21 +346,15 @@ stages:
     - awk '/^=+ ERRORS =+/{flag=1;next}/^=+.*=+$/{flag=0}flag' bin/tests/system/pytest.out.txt || true
 
 .shotgun: &shotgun_job
-  <<: *base_image
   <<: *api_pipelines_schedules_tags_triggers_web_triggering_rules
   stage: performance
-  script:
-    - if [ -z "$CI_COMMIT_TAG" ]; then export SHOTGUN_ROUNDS=1; else export SHOTGUN_ROUNDS=3; fi
-    - PIPELINE_ID=$(curl -s -X POST --fail
-        -F "token=$CI_JOB_TOKEN"
-        -F ref=main
-        -F "variables[SHOTGUN_TEST_VERSION]=['$CI_COMMIT_REF_NAME', '$BIND_BASELINE_VERSION']"
-        -F "variables[SHOTGUN_DURATION]=300"
-        -F "variables[SHOTGUN_ROUNDS]=$SHOTGUN_ROUNDS"
-        -F "variables[SHOTGUN_TRAFFIC_MULTIPLIER]=$SHOTGUN_TRAFFIC_MULTIPLIER"
-        -F "variables[SHOTGUN_SCENARIO]=$SHOTGUN_SCENARIO"
-        https://gitlab.isc.org/api/v4/projects/188/trigger/pipeline | jq .id)
-    - util/ci-wait-shotgun.py $PIPELINE_ID
+  trigger:
+    project: isc-projects/bind9-shotgun-ci
+    branch: main
+    strategy: depend
+  variables:
+    SHOTGUN_TEST_VERSION: "['$CI_COMMIT_REF_NAME', '$BIND_BASELINE_VERSION']"
+    SHOTGUN_DURATION: 300
   needs:
     - job: ci-variables
       artifacts: true
@@ -551,6 +545,7 @@ ci-variables:
     - if [ "$(sed -n -E "s|^m4_define\(\[bind_VERSION_PATCH\], ([0-9]+)\)dnl$|\1|p" configure.ac)" = "0" ]; then export BIND_BASELINE_BRANCH=$((BIND_BASELINE_BRANCH - 1 - (BIND_BASELINE_BRANCH % 2))); fi
     - BIND_BASELINE_VERSION="$(curl -s "https://gitlab.isc.org/api/v4/projects/1/repository/tags?search=^v9.${BIND_BASELINE_BRANCH}&order_by=version" | jq -r ".[0].name")"
     - echo "BIND_BASELINE_VERSION=$BIND_BASELINE_VERSION" >> ci_vars.env
+    - if [ -z "$CI_COMMIT_TAG" ]; then echo SHOTGUN_ROUNDS=1; else export SHOTGUN_ROUNDS=3; fi >> ci_vars.env
   needs:
     - job: autoreconf
       artifacts: true
@@ -1634,26 +1629,22 @@ respdiff-long-third-party:
 # allow re-use of the built container image. Otherwise, the jobs would do the
 # same builds in parallel rather than re-use the already built image.
 shotgun:udp:
-  <<: *shotgun_job
+  extends: .shotgun
   variables:
     SHOTGUN_SCENARIO: udp
     SHOTGUN_TRAFFIC_MULTIPLIER: 15
 
 shotgun:tcp:
-  <<: *shotgun_job
+  extends: .shotgun
   variables:
     SHOTGUN_SCENARIO: tcp
     SHOTGUN_TRAFFIC_MULTIPLIER: 6
-  when: delayed
-  start_in: 5 minutes
 
 shotgun:dot:
-  <<: *shotgun_job
+  extends: .shotgun
   variables:
     SHOTGUN_SCENARIO: dot
     SHOTGUN_TRAFFIC_MULTIPLIER: 3
-  when: delayed
-  start_in: 5 minutes
 
 # Parallel build in the "make" step is avoided since multiple jobs can be
 # executed concurrently on the same runner. This may present problems when one