CommandRequestExtendHeaderAppender
Copies each Command-Header-<key> request header into the command message header as <key>.
The prefix matches case-insensitively, since HTTP/2 sends header names in lower case. A key the framework reserves (ReservedCommandHeaderKeys: the operator, wait, local-first, trace and compensation keys …) is rejected with an IllegalArgumentException (IllegalArgument, 400) instead of being copied.