Audit log: log request host more robustly

[david-crespo]

Followup to #7339.

omicron/nexus/src/app/audit_log.rs

Lines 87 to 103 in 6ab7e96

	// A note on the handling of request URI: request.request.uri() is a
	// http::Uri, which contains the scheme and host only if they are in the
	// HTTP request line itself, i.e., only for HTTP/2 requests. So for HTTP/1.1
	// requests, all we'll have is a path. We are truncating it because it can
	// be arbitrarily long in theory, and we don't want to let people jam very
	// long strings into the DB.
	//
	// We could use the authority_for_request helper defined elsewhere to pull
	// the authority out of either the URI or the host header as appropriate
	// and log that in a dedicated column. In that case I think we would want
	// to log uri().path_and_query() instead of the full URI -- the only problem
	// is that path_and_query() returns an option, so we'd need to decide what
	// to fall back to, though in practice I don't think it's possible for it to
	// come back as `None` because every operation we audit log has a path.
	//
	// We should also consider redacting query strings or at least building in
	// some tooling to help us make sure we're not logging anything sensitive.