[Tests] Setup needed for Connection Pool reliability testing

Connection Pool reliability testing is needed for pool validation, specially with the new incoming connection pool design work, led by @mdaigle #3356.

This test framework should cover connection pool behaviors under stress, high CPU load and concurrent runs. Some of the initial work came through PR #3632 ([ConnectionPoolStressTest](https://github.com/dotnet/SqlClient/blob/d05100e99cdc06ca4347e66b3f96f8afa9b4276b/src/Microsoft.Data.SqlClient/tests/ManualTests/SQL/ConnectionPoolTest/ConnectionPoolStressTest.cs)) but is incomplete in its current state. It needs a new home, reworked and redesigned to do more elaborate testing.