healthcheck: report API key status

[josephjclark]

When we call the healthcheck endpoint, we should report on the status of API keys. Whether they've been set and whether they're responding

We need a function that, on server start, calls some simple diagnostic API on any relevant services (at the time of writing it would be pinecone and openai). We need to find some simple no-op endpoint we can call just to validate the authentication

We should log the result on startup, maybe on the index page, and at the healthcheck endpoint