Support selecting multiple test suite

[mdelapenya]

We currently use a select in Jenkins UI, so only a single element is accepted when running this job. So upstream triggers can only pass one test suite (helm, integrations or metricbeat at this moment).

We'd like to pass a comma-separated list so an upstream job is possible to tell the downstream to run helm && metricbeat, i.e.

[mdelapenya]

When calling from Beats/packaging job, we'd like to be able to:

• when elastic-agent is modified in Beats, trigger the ingest-manager test suite
• when metricbeat is modified in Beats, trigger the helm, integrations and ingest-manager test suites
• when filebeat is modified in Beats, trigger the helm and ingest-manager test suites
• when libbeat is modified in Beats, trigger all the test suites