Handle exception when unable to connect to Home Assistant

[stintel]

When WAS Command Endpoint is enabled and WAS cannot connect to Home Assistant (e.g. due to wrong token), we hit a HTTP 500 when saving the configuration:

[2025-02-25T22:11:51] INFO:     10.50.16.10:41200 - 'POST /api/config?type=config&apply=0 HTTP/1.1' 500 Internal Server Error
[2025-02-25T22:11:51] ERROR:    Exception in ASGI application
Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/requests/models.py", line 971, in json
    return complexjson.loads(self.text, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/json/__init__.py", line 346, in loads
    return _default_decoder.decode(s)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/json/decoder.py", line 340, in decode
    raise JSONDecodeError("Extra data", s, end)
json.decoder.JSONDecodeError: Extra data: line 1 column 4 (char 3)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/local/lib/python3.12/site-packages/uvicorn/protocols/http/httptools_impl.py", line 426, in run_asgi
    result = await app(  # type: ignore[func-returns-value]
             ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/uvicorn/middleware/proxy_headers.py", line 84, in __call__
    return await self.app(scope, receive, send)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/fastapi/applications.py", line 292, in __call__
    await super().__call__(scope, receive, send)
  File "/usr/local/lib/python3.12/site-packages/starlette/applications.py", line 122, in __call__
    await self.middleware_stack(scope, receive, send)
  File "/usr/local/lib/python3.12/site-packages/starlette/middleware/errors.py", line 184, in __call__
    raise exc
  File "/usr/local/lib/python3.12/site-packages/starlette/middleware/errors.py", line 162, in __call__
    await self.app(scope, receive, _send)
  File "/usr/local/lib/python3.12/site-packages/starlette/middleware/cors.py", line 91, in __call__
    await self.simple_response(scope, receive, send, request_headers=headers)
  File "/usr/local/lib/python3.12/site-packages/starlette/middleware/cors.py", line 146, in simple_response
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.12/site-packages/starlette/middleware/exceptions.py", line 79, in __call__
    raise exc
  File "/usr/local/lib/python3.12/site-packages/starlette/middleware/exceptions.py", line 68, in __call__
    await self.app(scope, receive, sender)
  File "/usr/local/lib/python3.12/site-packages/fastapi/middleware/asyncexitstack.py", line 20, in __call__
    raise e
  File "/usr/local/lib/python3.12/site-packages/fastapi/middleware/asyncexitstack.py", line 17, in __call__
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.12/site-packages/starlette/routing.py", line 718, in __call__
    await route.handle(scope, receive, send)
  File "/usr/local/lib/python3.12/site-packages/starlette/routing.py", line 276, in handle
    await self.app(scope, receive, send)
  File "/usr/local/lib/python3.12/site-packages/starlette/routing.py", line 66, in app
    response = await func(request)
               ^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/fastapi/routing.py", line 273, in app
    raw_response = await run_endpoint_function(
                   ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/fastapi/routing.py", line 190, in run_endpoint_function
    return await dependant.call(**values)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/app/routers/config.py", line 86, in api_post_config
    init_command_endpoint(request.app)
  File "/app/app/internal/command_endpoints/main.py", line 37, in init_command_endpoint
    app.command_endpoint = HomeAssistantWebSocketEndpoint(app, host, port, tls, token)
                           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/app/app/internal/command_endpoints/ha_ws.py", line 33, in __init__
    if not self.is_supported():
           ^^^^^^^^^^^^^^^^^^^
  File "/app/app/internal/command_endpoints/ha_ws.py", line 46, in is_supported
    if "assist_pipeline" in response.json():
                            ^^^^^^^^^^^^^^^
  File "/usr/local/lib/python3.12/site-packages/requests/models.py", line 975, in json
    raise RequestsJSONDecodeError(e.msg, e.doc, e.pos)
requests.exceptions.JSONDecodeError: Extra data: line 1 column 4 (char 3)

Handle this cleanly.