Search queries are not executed concurrently

Customers think we don't do concurrent execution of the search queries, and hence, users need to wait for other users to finalise their search.

At 19:00 minute of the recording: https://magnolia-cms.zoom.us/rec/share/Fkd9YuJdMIyisdTwKIDZh7MDGe3GcKMNWEsXT-1u1mLKsx8-EM65JoiBDhChZfFx.DVTpqAofUU7BsisO

AC:

• Investigate previous discovery and either confirm/infirm the following statement: "Multiple threads trying to get the same session on the same workspace will give you badtimes (IIRC throws an exception on the second thread)."
• If possible, remove the Semaphore lock, and make the concurrency configurable 
  • Measure and record the times before the change and after the change in this ticket using the big data environment: https://www.notion.so/magnoliacms/Monitoring-and-tracking-metrics-d6c3037f7a584aa79911ecaf3d3bd22f
• During investigation, fill MGNLPER-190 as needed

Dev notes: source stackOverflow

• javax.jcr.Session is not thread-safe, so if you're going to use a Session to handle multiple requests, you have to be sure that a Session is only being used in processing one request at a time. In other words, you'd some sort of pool of Sessions objects.
• Session is stateful, so any information loaded by one session might be kept until the Session is refreshed or closed.
• Session is for a specific user. If each incoming request might be associated with different users, you may be leaking privileges and data.

Other notes: https://jackrabbit.apache.org/jcr/concurrency-control.html