branch-2.1: [fix](mow) fix potential mem leak for DeleteBitmap::AggCache #52596 (#52613)

Cherry-picked from #52596

Co-authored-by: zhannngchen <zhangchen@selectdb.com>

be/src/olap/tablet_meta.h

@@ -536,6 +536,12 @@ public:
             std::call_once(once, [size_in_bytes] {
                 auto* tmp = new AggCachePolicy(size_in_bytes);
                 AggCache::s_repr.store(tmp, std::memory_order_release);
+
+                // release the sigleton instance at program exit
+                std::atexit([] {
+                    auto* ptr = AggCache::s_repr.exchange(nullptr, std::memory_order_acquire);
+                    delete ptr;
+                });
             });
 
             while (!s_repr.load(std::memory_order_acquire)) {