Support setting the path for hdfs

[kyungwan-nam]

#3526

[tangyoupeng]

Could you also add some docs for this pr?
https://github.com/juicedata/juicefs/blob/main/docs/en/guide/how_to_set_up_object_storage.md

[codecov-commenter]

Codecov Report

Patch coverage has no change and project coverage change: -8.83 ⚠️

Comparison is base (461017f) 55.93% compared to head (a9ee2e0) 47.11%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3528      +/-   ##
==========================================
- Coverage   55.93%   47.11%   -8.83%     
==========================================
  Files         149      149              
  Lines       36368    36374       +6     
==========================================
- Hits        20342    17137    -3205     
- Misses      13787    17199    +3412     
+ Partials     2239     2038     -201     

Impacted Files	Coverage Δ
pkg/object/hdfs.go	0.77% <0.00%> (-65.36%)	⬇️

... and 57 files with indirect coverage changes

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[kyungwan-nam]

@tangyoupeng
Thank you for reviewing.
I updated the document about it.