REORG: include: move sample.h to haproxy/sample{,-t}.h

This one is particularly tricky to move because everyone uses it
and it depends on a lot of other types. For example it cannot include
arg-t.h and must absolutely only rely on forward declarations to avoid
dependency loops between vars -> sample_data -> arg. In order to address
this one, it would be nice to split the sample_data part out of sample.h.
diff --git a/include/haproxy/auth.h b/include/haproxy/auth.h
index 3eafa41..d7ec2f7 100644
--- a/include/haproxy/auth.h
+++ b/include/haproxy/auth.h
@@ -17,7 +17,7 @@
 #include <haproxy/auth-t.h>
 #include <haproxy/api.h>
 #include <haproxy/pattern-t.h>
-#include <types/sample.h>
+#include <haproxy/sample-t.h>
 
 extern struct userlist *userlist;