h-a/whisper: Set writable cache dir for HF models

Whisper now needs a writable location for downloading models from
Hugging Face Hub.  The default location is `~/.cache/huggingface/hub`,
but this is not writable in our container.  The path can be controlled
via one of several environment variables, but we're setting `HF_HOME` as
it is sets the top level directory for several related paths.

home-assistant/whisper.yaml

@@ -42,6 +42,9 @@ spec:
         args:
         - --model=base
         - --language=en
+        env:
+        - name: HF_HOME
+          value: /data/hf.cache
         ports:
         - containerPort: 10300
           name: wyoming