Introduce a tool to start multiple FEs on single node.
Use case:
```
$ ./multi-fe
./multi-fe start|stop|clean [OPTIONS ...]
start -n <NUM> -l <LIBRARY_PATH> -p <BASE_PORT>
Start the FE cluster.
-n The number of FEs.
-l The FE library path (default: doris/output/fe/lib)
-p The base port to generate all needed ports (default: 9030).
stop Stop the FE cluster.
clean Stop the data (rm -rf "$(pwd)"/fe*).
```