[Security] [SecEngProd] Added a security solution pipeline entrypoint (…

…elastic#175435)

## Summary

This PR is only introducing the entrypoint for a new pipeline for
Security Solution where all the tests which run in the `pull-request`
pipeline will be running against a real deployment and not against a
dockerized one.

.buildkite/scripts/pipelines/security_solution_ess/pipeline.sh

@@ -0,0 +1,5 @@
+#!/bin/bash
+
+set -euo pipefail
+
+echo "Inside the security solution pipeline"