store: set RocksDB max_total_wal_size

Summary:
We have seen some users with very long startup times due to very large WAL
files on disk. Let's reduce the WAL size to make sure EdenFS startup is always
fast.

Reviewed By: chadaustin

Differential Revision: D34260876

fbshipit-source-id: dc4d94484c7afdc8350b3cbb862cfb8b4b8aa60b

eden/fs/store/RocksDbLocalStore.cpp

@@ -241,6 +241,9 @@ rocksdb::Options getRocksdbOptions() {
   // Automatically create column families as we define new ones.
   options.create_missing_column_families = true;
 
+  // Make sure we never hold more than 128MB onto the WAL
+  options.max_total_wal_size = 128 * 1024 * 1024;
+
   return options;
 }