MINOR: version: mention that it's stable now

This version will be maintained up to around Q1 2022.
diff --git a/include/haproxy/version.h b/include/haproxy/version.h
index f2bf12a..4ec2267 100644
--- a/include/haproxy/version.h
+++ b/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 2022."
 #endif
 
 #ifdef CONFIG_PRODUCT_URL_BUGS