Do not redirect /api/v1/ URLs from HTTP to HTTPS

[alexmv]

We currently do this redirect at the nginx level; we should adjust nginx to let through requests to /api/v1/ over HTTP, and add a middleware which detects those and renders a constant "The Zulip API is only accessible over HTTPS" error, potentially along with a "your API key should be considered compromised, and rotated" if the request had a valid API key.

See this blog post, CZO thread