Tune eviction threshold in cache mode

[adiholden]

Today eviction starts on 90% memory usage in cache mode
If we set deny_oom_flag to lower than 90% then we reject writes and no eviction is taking place.
We need to set the threshold so it will take into account this flag

[adiholden]

flag names : rss_oom_deny_ratio oom_deny_ratio
pytest for reference how to check eviction : test_heartbeat_eviction_propagation

[BagritsevichStepan]

Another issue (#4139) was created for this task

[BagritsevichStepan]

Current problem: mimalloc does not release RSS memory back to the OS. Alternatively, the OS might not be reclaiming this freed memory due to a lack of memory pressure. This is a common issue in mimalloc, and I have tried various options, but only one of them helped.

The more info is provided in this PR: #4772