MINOR: proxy: Store monitor_uri as a `struct ist`

The monitor_uri is already processed as an ist in `http_wait_for_request`, lets
also just store it as such.

see 0643b0e7e ("MINOR: proxy: Make `header_unique_id` a `struct ist`") for a
very similar past commit.
diff --git a/include/haproxy/proxy-t.h b/include/haproxy/proxy-t.h
index 421f900..13e722f 100644
--- a/include/haproxy/proxy-t.h
+++ b/include/haproxy/proxy-t.h
@@ -322,8 +322,7 @@
 	int srvtcpka_cnt;                       /* The maximum number of keepalive probes TCP should send before dropping the connection. (server side) */
 	int srvtcpka_idle;                      /* The time (in seconds) the connection needs to remain idle before TCP starts sending keepalive probes. (server side) */
 	int srvtcpka_intvl;                     /* The time (in seconds) between individual keepalive probes. (server side) */
-	int monitor_uri_len;			/* length of the string above. 0 if unused */
-	char *monitor_uri;			/* a special URI to which we respond with HTTP/200 OK */
+	struct ist monitor_uri;			/* a special URI to which we respond with HTTP/200 OK */
 	struct list mon_fail_cond;              /* list of conditions to fail monitoring requests (chained) */
 	struct {				/* WARNING! check proxy_reset_timeouts() in proxy.h !!! */
 		int client;                     /* client I/O timeout (in ticks) */
diff --git a/src/cfgparse-listen.c b/src/cfgparse-listen.c
index 5deec5e..eb58b2eb 100644
--- a/src/cfgparse-listen.c
+++ b/src/cfgparse-listen.c
@@ -575,13 +575,10 @@
 			goto out;
 		}
 
-		free(curproxy->monitor_uri);
-		curproxy->monitor_uri_len = strlen(args[1]);
-		curproxy->monitor_uri = calloc(1, curproxy->monitor_uri_len + 1);
-		if (!curproxy->monitor_uri)
+		istfree(&curproxy->monitor_uri);
+		curproxy->monitor_uri = istdup(ist(args[1]));
+		if (!isttest(curproxy->monitor_uri))
 			goto alloc_error;
-		memcpy(curproxy->monitor_uri, args[1], curproxy->monitor_uri_len);
-		curproxy->monitor_uri[curproxy->monitor_uri_len] = '\0';
 
 		goto out;
 	}
diff --git a/src/http_ana.c b/src/http_ana.c
index f33eb77..b60927e 100644
--- a/src/http_ana.c
+++ b/src/http_ana.c
@@ -203,9 +203,8 @@
 	 * used. It is a workaround to let HTTP/2 health-checks work as
 	 * expected.
 	 */
-	if (unlikely(sess->fe->monitor_uri_len != 0)) {
-		const struct ist monitor_uri = ist2(sess->fe->monitor_uri,
-		                                    sess->fe->monitor_uri_len);
+	if (unlikely(isttest(sess->fe->monitor_uri))) {
+		const struct ist monitor_uri = sess->fe->monitor_uri;
 		struct http_uri_parser parser = http_uri_parser_init(htx_sl_req_uri(sl));
 
 		if ((istptr(monitor_uri)[0] == '/' &&
diff --git a/src/proxy.c b/src/proxy.c
index dbcab47..79aa3f4 100644
--- a/src/proxy.c
+++ b/src/proxy.c
@@ -156,7 +156,7 @@
 	free(p->lbprm.arg_str);
 	free(p->server_state_file_name);
 	free(p->capture_name);
-	free(p->monitor_uri);
+	istfree(&p->monitor_uri);
 	free(p->rdp_cookie_name);
 	free(p->invalid_rep);
 	free(p->invalid_req);
@@ -1274,7 +1274,7 @@
 		ha_warning("cookie will be ignored for %s '%s' (needs 'mode http').\n",
 			   proxy_type_str(curproxy), curproxy->id);
 	}
-	if (curproxy->monitor_uri != NULL) {
+	if (isttest(curproxy->monitor_uri)) {
 		ha_warning("monitor-uri will be ignored for %s '%s' (needs 'mode http').\n",
 			   proxy_type_str(curproxy), curproxy->id);
 	}
@@ -1436,7 +1436,7 @@
 	ha_free(&defproxy->cookie_attrs);
 	ha_free(&defproxy->lbprm.arg_str);
 	ha_free(&defproxy->capture_name);
-	ha_free(&defproxy->monitor_uri);
+	istfree(&defproxy->monitor_uri);
 	ha_free(&defproxy->defbe.name);
 	ha_free(&defproxy->conn_src.iface_name);
 	ha_free(&defproxy->fwdfor_hdr_name); defproxy->fwdfor_hdr_len = 0;
@@ -1711,9 +1711,8 @@
 		curproxy->timeout.tarpit = defproxy->timeout.tarpit;
 		curproxy->timeout.httpreq = defproxy->timeout.httpreq;
 		curproxy->timeout.httpka = defproxy->timeout.httpka;
-		if (defproxy->monitor_uri)
-			curproxy->monitor_uri = strdup(defproxy->monitor_uri);
-		curproxy->monitor_uri_len = defproxy->monitor_uri_len;
+		if (isttest(defproxy->monitor_uri))
+			curproxy->monitor_uri = istdup(defproxy->monitor_uri);
 		if (defproxy->defbe.name)
 			curproxy->defbe.name = strdup(defproxy->defbe.name);