In case an error is returned when calling search_shards on a remote
cluster, which will lead to throwing an exception in the coordinating
node, we should make sure that the status code returned by the
coordinating node is the same as the one returned by the remote
cluster. Up until now a 500 - Internal Server Error was always
returned. This commit changes this behaviour so that for instance if an
index is not found, which causes an 404, a 404 is also returned by the
coordinating node to the client.
Closes#27461
70749e01c4