Add TAP tests for log_lock_waits

Add TAP tests for log_lock_waits

This commit updates 011_lock_stats.pl to verify log_lock_waits behavior.

The tests check that messages are emitted both when a wait occurs and
when the lock is acquired, and that the "still waiting for" message is logged
exactly once per wait, even if the backend wakes up during the wait.

The latter covers the behavior introduced by commit fd6ecbfa75f.

Author: Hüseyin Demir <huseyin.d3r@gmail.com>
Co-authored-by: Fujii Masao <masao.fujii@gmail.com>
Discussion: https://postgr.es/m/CAB5wL7YB1my9W5k5i=SY+=sTjeozyJ0YkvGXrVfeDNzuRkoTPg@mail.gmail.com