ci(buildkite): change to concurrency gates (#1752)

* ci(buildkite): change to concurrency gates

Continuation of #1751.

* ci(buildkite): optimise concurrency gates

.buildkite/steps/buildimages.sh

@@ -38,3 +38,12 @@ EOF
 fi
   done
 done
+cat << EOF
+
+  - wait
+
+  - label: ":vertical_traffic_light: Build Concurrency Gate"
+    command: "echo End of concurrency gate"
+    concurrency: 3
+    concurrency_group: "builds"
+EOF

.buildkite/steps/e2etests.sh

@@ -25,3 +25,12 @@ cat << EOF
 EOF
 fi
 done
+cat << EOF
+
+  - wait
+
+  - label: ":vertical_traffic_light: Test Concurrency Gate"
+    command: "echo End of concurrency gate"
+    concurrency: 3
+    concurrency_group: "tests"
+EOF