1. the real value of BE config `file_cache_max_file_reader_cache_size` will be the 1/3 of process's max open file number.
2. use thread pool to create or init the file cache concurrently.
To solve the issue that when there are lots of files in file cache dir, the starting time of BE will be very slow because
it will traverse all file cache dirs sequentially.
Use weak_ptr to cache the file handle of file segment. The max cached number of file handles can be configured by `file_cache_max_file_reader_cache_size`, default `1000000`.
Users can inspect the number of cached file handles by request BE metrics: `http://be_host:be_webserver_port/metrics`:
```
# TYPE doris_be_file_cache_segment_reader_cache_size gauge
doris_be_file_cache_segment_reader_cache_size{path="/mnt/datadisk1/gaoxin/file_cache"} 2500
```
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.
Currently, there are some useless includes in the codebase. We can use a tool named include-what-you-use to optimize these includes. By using a strict include-what-you-use policy, we can get lots of benefits from it.
Save cached file segment into path like `cache_path / hash(filepath).substr(0, 3) / hash(filepath) / offset`
to prevent too many directories in `cache_path`.
The main purpose of this pr is to import `fileCache` for lakehouse reading remote files.
Use the local disk as the cache for reading remote file, so the next time this file is read,
the data can be obtained directly from the local disk.
In addition, this pr includes a few other minor changes
Import File Cache:
1. The imported `fileCache` is called `block_file_cache`, which uses lru replacement policy.
2. Implement a new FileRereader `CachedRemoteFilereader`, so that the logic of `file cache` is hidden under `CachedRemoteFilereader`.
Other changes:
1. Add a new interface `fs()` for `FileReader`.
2. `IOContext` adds some statistical information to count the situation of `FileCache`
Co-authored-by: Lightman <31928846+Lchangliang@users.noreply.github.com>
