MINOR: server: enable slowstart for dynamic server

Enable the 'slowstart' keyword for dynamic servers. The slowstart task
is allocated in 'add server' handler if slowstart is used.

As the server is created in disabled state, there is no need to start
the task. The slowstart task will be automatically started on the first
'enable server' invocation.

doc/management.txt

@@ -1548,6 +1548,7 @@ add server <backend>/<server> [args]*
   - send-proxy-v2
   - send-proxy-v2-ssl
   - send-proxy-v2-ssl-cn
+  - slowstart
   - sni
   - source
   - ssl

src/server.c

@@ -1673,7 +1673,7 @@ static struct srv_kw_list srv_kws = { "ALL", { }, {
 	{ "resolvers",           srv_parse_resolvers,           1,  1,  0 }, /* Configure the resolver to use for name resolution */
 	{ "send-proxy",          srv_parse_send_proxy,          0,  1,  1 }, /* Enforce use of PROXY V1 protocol */
 	{ "send-proxy-v2",       srv_parse_send_proxy_v2,       0,  1,  1 }, /* Enforce use of PROXY V2 protocol */
-	{ "slowstart",           srv_parse_slowstart,           1,  1,  0 }, /* Set the warm-up timer for a previously failed server */
+	{ "slowstart",           srv_parse_slowstart,           1,  1,  1 }, /* Set the warm-up timer for a previously failed server */
 	{ "source",              srv_parse_source,             -1,  1,  1 }, /* Set the source address to be used to connect to the server */
 	{ "stick",               srv_parse_stick,               0,  1,  0 }, /* Enable stick-table persistence */
 	{ "tfo",                 srv_parse_tfo,                 0,  1,  1 }, /* enable TCP Fast Open of server */
@@ -4660,6 +4660,10 @@ static int cli_parse_add_server(char **args, char *payload, struct appctx *appct
 		srv->agent.state &= ~CHK_ST_ENABLED;
 	}
 
+	/* Init slowstart if needed. */
+	if (init_srv_slowstart(srv))
+		goto out;
+
 	/* Attach the server to the end of the proxy linked list. Note that this
 	 * operation is not thread-safe so this is executed under thread
 	 * isolation.