fix #5997: metrics: influxdb: fall back to the ready endpoint in connection test

The connection test for InfluxDB over HTTP(S) queries the '/health'
endpoint. The InfluxDB v2 listener of Telegraf only has it since
version 1.36, older versions only provide '/api/v2/ready'. So adding
such a listener as metric server fails with '404 Not Found', although
writing metrics to it would work.

If '/health' is not found, query '/api/v2/ready' instead. Other errors,
like an invalid token, are still reported right away.

Signed-off-by: Michal Fox <me@dualfroz.com>

PVE/Status/InfluxDB.pm

@@ -267,6 +267,11 @@ sub test_connection {
         }
         my $response = $ua->get($url);
 
+        # the InfluxDB v2 listener of Telegraf before 1.36 only has the ready endpoint
+        if ($response->code == 404) {
+            $response = $ua->get(_get_v2url($cfg, "ready"));
+        }
+
         if (!$response->is_success) {
             my $err = $response->status_line;
             die "$err\n";