[RELEASE] Released version 2.9-dev0

Released version 2.9-dev0 with the following main changes :
    - MINOR: version: mention that it's development again

CHANGELOG

@@ -1,6 +1,9 @@
 ChangeLog :
 ===========
 
+2023/05/31 : 2.9-dev0
+    - MINOR: version: mention that it's development again
+
 2023/05/31 : 2.8.0
     - MINOR: compression: Improve the way Vary header is added
     - BUILD: makefile: search for SSL_INC/wolfssl before SSL_INC

VERSION

@@ -1 +1 @@
-2.8.0
+2.9-dev0

doc/configuration.txt

@@ -2,7 +2,7 @@
                                 HAProxy
                           Configuration Manual
                          ----------------------
-                              version 2.8
+                              version 2.9
                               2023/05/31
 
 

doc/intro.txt

@@ -1,7 +1,7 @@
                              -----------------------
                               HAProxy Starter Guide
                              -----------------------
-                                   version 2.8
+                                   version 2.9
 
 
 This document is an introduction to HAProxy for all those who don't know it, as

doc/management.txt

@@ -1,7 +1,7 @@
                              ------------------------
                              HAProxy Management Guide
                              ------------------------
-                                   version 2.8
+                                   version 2.9
 
 
 This document describes how to start, stop, manage, and troubleshoot HAProxy,

include/haproxy/version.h

@@ -33,7 +33,7 @@
 #ifdef  CONFIG_PRODUCT_BRANCH
 #define PRODUCT_BRANCH    CONFIG_PRODUCT_BRANCH
 #else
-#define PRODUCT_BRANCH   "2.8"
+#define PRODUCT_BRANCH   "2.9"
 #endif
 
 #ifdef  CONFIG_PRODUCT_STATUS