MINOR: version: mention that 3.1 is stable now

This version will be maintained up to around Q1 2026. The INSTALL file
also mentions it.

INSTALL

@@ -1,13 +1,12 @@
 Installation instructions for HAProxy
 =====================================
 
-This is a development version, so it is expected to break from time to time,
-to add and remove features without prior notification and it should not be used
-in production, unless you're an experienced user and are willing to follow
-weekly updates. If you are not used to build from sources or if you are not
-used to follow updates then it is recommended that instead you use the packages
-provided by your software vendor or Linux distribution. Most of them are taking
-this task seriously and are doing a good job at backporting important fixes.
+HAProxy 3.1 is a stable version, which means that it will get fixes for bugs as
+they are discovered till around Q1 2026 and should not receive new features.
+This version is mostly suited at experienced users who are willing to quickly
+follow updates. New users are encouraged to use long term supported versions
+such as the ones provided by their software vendor or Linux distribution, as
+such versions require far less common updates.
 
 If for any reason you would prefer a different version than the one packaged
 for your system, you want to be certain to have all the fixes or to get some

include/haproxy/version.h

@@ -39,7 +39,7 @@
 #ifdef  CONFIG_PRODUCT_STATUS
 #define PRODUCT_STATUS    CONFIG_PRODUCT_STATUS
 #else
-#define PRODUCT_STATUS   "Status: development branch - not safe for use in production."
+#define PRODUCT_STATUS   "Status: stable branch - will stop receiving fixes around Q1 2026."
 #endif
 
 #ifdef CONFIG_PRODUCT_URL_BUGS