fix: clarify TSA DNS/network/firewall validation failure

Signed-off-by: Vitor Mattos <1079143+vitormattos@users.noreply.github.com>

Author: vitormattos

lib/Service/TsaValidationService.php

@@ -62,7 +62,7 @@ private function validateTsaHostResolution(string $tsaUrl): void {
 		}
 
 		if (!@gethostbyname($host) || gethostbyname($host) === $host) {
-			throw new LibresignException('Timestamp Authority (TSA) service is unavailable or misconfigured: ' . $tsaUrl);
+			throw new LibresignException('Timestamp Authority (TSA) service is unavailable. Check DNS/network/firewall connectivity from this server: ' . $tsaUrl);
 		}
 	}
 }