Fix - rasql polygonize doesn't work because temp folder doesn't exist

[Bang Pham Huu]

Because this temp folder /tmp/rasdaman/polygonize/ does not exist, then, the polygonize query doesn't work:

 [INFO] - 2023-12-10 20:29:50,395: Request: 'select polygonize(c, "ESRI Shapefile") from test_mr as c'... parsing... checking semantics... evaluating... [ERROR] - 2023-12-10 20:29:50,395, qlparser/qtpolygonize.cc:477: 

Error creating directory of base filename /tmp/rasdaman/polygonize/
no explanation text available for error code 723

Also update the queries example in ​https://doc.rasdaman.org/04_ql-guide.html#polygonize-operation

to have this format:

rasql -q 'select ...' --out file

otherwise, nobody knows how to get the output files from the query.