convert-hf : print output file name when completed (#8181)

convert-hf : print output file name when completed (#8181)

* convert-hf : print output file name when completed

This commit adds the output file name to the log message when the
conversion is completed.

The motivation for this change is that when `--outfile` option is not
specified it migth not be obvious where the output file is written.

With this change the output of running the script will be something like
the following:
```console
INFO:hf-to-gguf:Model successfully exported to models/gemma-2-9b-it.gguf.
```

Signed-off-by: Daniel Bevenius <redacted>
* squash! convert-hf : print output file name when completed

Updates the output of to support printing the directory if the output is
split into multiple files. Also the output file name is now retrieved
from the model_instance object.

Signed-off-by: Daniel Bevenius <redacted>
* squash! convert-hf : print output file name when completed

Use parent attribute of Path object and string interpolation.

Signed-off-by: Daniel Bevenius <redacted>
* squash! convert-hf : print output file name when completed

Use os.sep instead of hardcoding the path separator.

Signed-off-by: Daniel Bevenius <redacted>
---------

Signed-off-by: Daniel Bevenius <redacted>