Revisit location for installing additional parquet index files

[fedorov]

@jcfr here we are downloading additional parquet files on demand by the user, and saving them into the same location as the original files installed as part of idc-index-data installation.

@vkt1414 raised a valid concern that this is probably not the best practice. Based on your experience, can you advise where such runtime-installed files should be saved? Somewhere under user home directory?