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

[josephjclark]

On reflection I don't think this can go on the healthcheck because it'll be slow to run. And we want healthcheck to be fast.

So we add a /status endpoint. When that page is loaded, we'll call out to each connected service and just "ping" it somehow to make sure it works

I think right now it's just pinecone and openai that the server natively supports. So we need to work out a cheap test from both systems.

The status page should return some simple HTML or just JSON data showing the status of each key. I suppose HTML by default but it should support a header of Accept: application/json.