MINOR: version: report the version status in "haproxy -v"

As discussed on Discourse here:

    https://discourse.haproxy.org/t/haproxy-branch-support-lifetime/4466

it's not always easy for end users to know the lifecycle of the version
they are using. This patch introduces a "Status" line in the output of
"haproxy -vv" indicating whether it's a development, stable, long-term
supported version, possibly with an estimated end of life for the branch
when it can be anticipated (e.g. for stable versions). This field should
be adjusted when creating a major release to reflect the new status.

It may make sense to backport this to other branches to clarify the
situation.

include/common/version.h

@@ -36,6 +36,12 @@
 #define PRODUCT_BRANCH   "2.1"
 #endif
 
+#ifdef  CONFIG_PRODUCT_STATUS
+#define PRODUCT_STATUS    CONFIG_PRODUCT_STATUS
+#else
+#define PRODUCT_STATUS   "Status: development branch - not safe for use in production."
+#endif
+
 #ifdef  CONFIG_PRODUCT_URL
 #define PRODUCT_URL    CONFIG_PRODUCT_URL
 #else

src/haproxy.c

@@ -543,7 +543,8 @@ void hap_register_per_thread_free(int (*fct)())
 
 static void display_version()
 {
-	printf("HA-Proxy version %s %s - https://haproxy.org/\n", haproxy_version, haproxy_date);
+	printf("HA-Proxy version %s %s - https://haproxy.org/\n"
+	       PRODUCT_STATUS "\n", haproxy_version, haproxy_date);
 }
 
 static void display_build_opts()