Feature "Apply unpersisted raft log" may cause OOM

[glorv]

PR #16626 introduced a new mechanism that allows apply committed raft log before persistence. But it also brings some side-effect:

• Block region cache eviction. Because only persisted logs can be evicted. This may lead to more memory usage and cause OOM.
• Block raft log GC. This may lead to more disk space usage in raft-engine.

This issue is created for tracking these side-effects so we may need to optimize them in the near future.