Introduces WithAdoptCfRayHeader option to allow HTTP handlers to adopt
incoming Cf-Ray headers as correlation IDs. When enabled, the handler
will prefer Cf-Ray over X-Request-ID for correlation ID propagation.

This is particularly useful for services behind Cloudflare where the
Ray-ID provides a unique request identifier across the CDN.

Add support for adopting Cloudflare Ray-ID as correlation ID

See merge request !223



Merged-by: Igor <iwiedler@gitlab.com>
Approved-by: Andrew Newdigate <andrew@gitlab.com>
Reviewed-by: João Pereira <jpereira@gitlab.com>