[rswalkden]

Fixes response handling when captcha validation fails, and adds protector API status and latency to ingest records.

Changes

Captcha validation (handleCaptcha)

• The response status is now set before the body is written. Previously the headers went out as 200 first, and nginx logged attempt to set status ... via ngx.exit after sending out the response status 200.
• When the protector API call fails (timeout, connection error), the client now gets a 502 instead of an unhandled Lua error.
• Protector 2xx and 4xx responses are passed through with their Content-Type. Any other status returns a generic 502.

Ingest

• Added ProtectorStatus: the HTTP status returned by the protector API, or 0 if no response was received. The field is omitted when no protector call was made.
• Added ProtectorLatencyMs: how long the protector API call took, in milliseconds.
• BytesReceived now uses $request_length and is always a number. It was always 0 before, because $bytes_received only exists in nginx's stream module.