Add support for custom HOME_DIR

[wsntxxn]

Nowadays we often mount a filesystem on clusters so that cache directories for downloading and saving models are better set on mounted filesystems. Therefore I prefer customizing WESPEAKER_HOME by something like this:

modifying https://github.com/wenet-e2e/wespeaker/blob/master/wespeaker/cli/hub.py#L106

model_dir = os.path.join(Path.home(), ".wespeaker", lang)

to

model_dir = os.path.join(os.environ.get("WESPEAKER_HOME", Path.home()), ".wespeaker", lang))

and other places with reference to the home directory.

[cdliang11]

Good! Welcome pr @wsntxxn