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/types/spoe.h b/include/types/spoe.h
index f08b9ad..fdaba93 100644
--- a/include/types/spoe.h
+++ b/include/types/spoe.h
@@ -32,7 +32,7 @@
 #include <haproxy/freq_ctr-t.h>
 #include <types/log.h>
 #include <types/proxy.h>
-#include <types/sample.h>
+#include <haproxy/sample-t.h>
 #include <types/stream.h>
 #include <types/task.h>