common : refactor '-o' option (#12278)
As discussed in PR 'llama-tts : add -o option' (#12042):
* common_params : 'out_file' string is the only output file name parameter left in common_params. It's intended to be used in all example programs implementing an '-o' option.
* cvector-generator, export-lora, imatrix : default output filenames moved from 'common_params' to the 'main()' of each example program.
