1. Refactor file cache. Before refactor, the file cache config format is "[{"path":"/path/to/file_cache","normal":21474836480,"persistent":10737418240,"query_limit":10737418240}]" and now change to "[{"path":"/mnt/disk3/selectdb_cloud/file_cache","total_size":21474836480,"query_limit":10737418240}]". It will be simpler than before.
2. Support more strategy. Support file cache priority. The file cache will have three queue, name as 'index'/'normal'/'disposable'. We can avoid that the higher priority data is eliminate by the lower priority data.
1be5dac036