add slab rebalance timeout setting

Summary: Enabling slab release timeouts again and setting it to 10 minutes initially. Will gradually reduce it. Also added a setting to ucache, so ucache can disable/modify with a config change.

Reviewed By: rlyerly

Differential Revision: D90136674

fbshipit-source-id: da144ddd72a71da8eee12b81bcf46568f68424ca

Author: AlnisM

cachelib/allocator/CacheAllocatorConfig.h

@@ -603,7 +603,7 @@ class CacheAllocatorConfig {
 
   // the amount of time to wait for a slab to be released before giving up
   // and aborting the release. 0 means we will wait forever
-  std::chrono::milliseconds slabRebalanceTimeout{std::chrono::milliseconds(0)};
+  std::chrono::milliseconds slabRebalanceTimeout{std::chrono::minutes(10)};
 
   // If refcount is larger than this threshold, we will use shared_ptr
   // for handles in IOBuf chains.