Set up Buffer Pool Extension perf test

This is a task to prepare and run an early performance test for MDEV-31956 prototype.

The assumption here is that a developer will figure out specifics of how to test buffer pool extension performance and conduct some tests to ensure that the procedure is sound.

The deliverables of this task are:
1. A set of sepecific instructions that can be handed down to QA teams to set up test environments and conduct tests.

2. Test results for the existing prototype.

The inputs for this task are:

• protoype in branch bb-12.3-MDEV-31956-ext_buf_pool
• tests to be run should be same or analogous to those already run as part of PERF-560
• testing specifications given here