✨ Default target path -- implement replace extention function

[nicolay-r]

By looking at the following lines:

bulk-chain/bulk_chain/infer.py

Line 154 in 3cd47e9

cache_target = "".join(["_".join([join(CWD, basename(src_filepath)), llm.name(), schema.name]), f".sqlite"]) \

and

bulk-chain/bulk_chain/infer.py

Line 167 in 3cd47e9

output_target = "".join(["_".join([join(CWD, basename(src_filepath)), llm.name(), schema.name]), f".{tgt_ext}"]) \

adopts the same code.

We can copy the function for OsService that just replaces the extension