feat:support downloading files to specific directories

[xxxxibo]

What type of PR is this?

/kind feature

What this PR does / why we need it

support downloading files to specific directories

Which issue(s) this PR fixes

Fixes #

Special notes for your reviewer

./arctl -nrag-eval eval download —rag=test123 —application=def —dir=/tmp/xyz
copy source /rag-eval/a.csv to /tmp/xyz/a.csv
copy source /rag-eval/kaoqin.csv to/tmp/xyz/kaoqin.csv

root@ecs-4fc018ff-1ded-4c65-92dc-67dc1911226c:/tmp/xyz$ ls
a.csv  kaoqin.csv
root@ecs-4fc018ff-1ded-4c65-92dc-67dc1911226c:/tmp/xyz$ cat a.csv
a,a
b,b
c,c
d,d
e,e
f,f
g,g

[0xff-dev]

@dayuy pls review.

[bjwswang]

Thanks @xxxxibo @dayuy @0xff-dev