[ci] define matrix axes in code (#25360)

* [ci] define matrix axes in code

* [ci] add null exclude rule

* [ci] make script executable

* [ci] execute sub-scripts

* [ci] simplify job variable name

(cherry picked from commit 399c50c)

.ci/jobs.yml

@@ -0,0 +1,7 @@
+JOB:
+  - selenium
+  - intake
+  - x-pack
+
+# `~` is yaml for `null`
+exclude: ~

.ci/run.sh

@@ -0,0 +1,22 @@
+#!/usr/bin/env bash
+
+set -e
+
+# move to Kibana root
+cd "$(dirname "$0")/.."
+
+case "$JOB" in
+"selenium")
+  ./test/scripts/jenkins_selenium.sh
+  ;;
+"intake")
+  ./test/scripts/jenkins_unit.sh
+  ;;
+"x-pack")
+  ./test/scripts/jenkins_xpack.sh
+  ;;
+*)
+  echo "JOB '$JOB' is not implemented."
+  exit 1
+  ;;
+esac