source-http-ingest: support Okta "verification" challenge

[psFried]

Okta has this weird "verification" step that they do before they'll start sending webhooks. The process is described here, and there's some example code here. The TLDR is that they send a GET request with an x-okta-verification-challenge header, and we just need to echo back that header value as part of a JSON response. I can't imagine what's actually being verified with this, apart from the fact that the endpoint was specifically intending to support Okta webhooks. But it seems to be required, and is probably the easiest way for us to support capturing data from Okta.

I'm thinking that the easiest thing would be to just automatically create routes for all bindings that handle these GET requests. They'd be harmless in other usages of the connector, so I see no reason to conditionally enable them or add new endpoint configuration.