MINOR: startup: HAPROXY_STARTUP_VERSION contains the version used to start

HAPROXY_STARTUP_VERSION: contains the version used to start, in
master-worker mode this is the version which was used to start the
master, even after updating the binary and reloading.

This patch could be backported in every version since it is useful when
debugging.

(cherry picked from commit d4c0be6b20f5365dc00221b51face2a32cf4053b)
Signed-off-by: William Lallemand <wlallemand@haproxy.org>
(cherry picked from commit e0fb690416d2a5d383b427426caf3ebf23ca0d4a)
Signed-off-by: William Lallemand <wlallemand@haproxy.org>
(cherry picked from commit 978688bd26b1d704e6225ab88133986cd3cb34db)
[wla: init_early() doesn't exist, done in init()]
Signed-off-by: William Lallemand <wlallemand@haproxy.org>
(cherry picked from commit 616cbe6e09d76793beca7abaec2635384facb256)
Signed-off-by: Christopher Faulet <cfaulet@haproxy.com>
diff --git a/doc/configuration.txt b/doc/configuration.txt
index 0c23dd1..ec89073 100644
--- a/doc/configuration.txt
+++ b/doc/configuration.txt
@@ -753,6 +753,10 @@
 * HAPROXY_MASTER_CLI: In master-worker mode, listeners addresses of the master
   CLI, separated by semicolons.
 
+* HAPROXY_STARTUP_VERSION: contains the version used to start, in master-worker
+  mode this is the version which was used to start the master, even after
+  updating the binary and reloading.
+
 In addition, some pseudo-variables are internally resolved and may be used as
 regular variables. Pseudo-variables always start with a dot ('.'), and are the
 only ones where the dot is permitted. The current list of pseudo-variables is: