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

This one is particularly difficult to split because it provides all the
functions used to manipulate a proxy state and to retrieve names or IDs
for error reporting, and as such, it was included in 73 files (down to
68 after cleanup). It would deserve a small cleanup though the cut points
are not obvious at the moment given the number of structs involved in
the struct proxy itself.
diff --git a/src/stream_interface.c b/src/stream_interface.c
index 6b6b76d..67477a5 100644
--- a/src/stream_interface.c
+++ b/src/stream_interface.c
@@ -25,6 +25,7 @@
 #include <haproxy/connection.h>
 #include <haproxy/dynbuf.h>
 #include <haproxy/http_htx.h>
+#include <haproxy/proxy.h>
 #include <haproxy/stream_interface.h>
 #include <haproxy/tools.h>
 #include <haproxy/ticks.h>
@@ -32,7 +33,6 @@
 #include <haproxy/task.h>
 
 #include <haproxy/pipe.h>
-#include <proto/proxy.h>
 #include <proto/stream.h>
 
 #include <haproxy/pipe-t.h>