golang filter: do not clear route cache in the HeaderMap.Set API #33082
Description
instead, add a new API ClearRouteCache in FilterCallbacks
Reason:
Sometimes, we want to remove a prefix pattern in :path, without updating the route cache. otherwise, it may leads to route_not_found.
This is useful in API gateway scenarios when people add a base path in API spec, and we don't want other filters/backend upstream to know this base path exists.