reverseproxy: Handle "operation was canceled" errors (#3816)
reverseproxy: Handle "operation was canceled" errors (#3816)

* fix(caddy): Avoid "operation was canceled" errors

- Also add error handling for StatusGatewayTimeout

* revert(caddy): Revert 504 handling

- This will potentially break load balancing and health checks

* Handle client cancellation as different error

Co-authored-by: Matthew Holt <6e15340bc34d98c823445cca0475cc9127379d4b@users.noreply.github.com>
l3dlp/caddy,mholt/caddy,abiosoft/caddy,l3dlp/caddy,mholt/caddy,abiosoft/caddy,l3dlp/caddy