gitlab_runner: Set reasonable NOFILE limits to avoid bugs

The default limits cause issues as reported upstream[1][2], it also
breaks the mkinitcpio CI[3]. So match the limits set in systemd since
v240[4].

[1] https://github.com/moby/moby/issues/38814
[2] https://github.com/containerd/containerd/pull/7566
[3] archlinux/mkinitcpio/mkinitcpio@da223d2f
[4] https://github.com/systemd/systemd/blob/4f44d2c4f76922a4f48dd4473e6abaca40d7e555/NEWS#L6556-L6590

roles/gitlab_runner/files/daemon.json

@@ -2,5 +2,12 @@
 	"ipv6": true,
 	"fixed-cidr-v6": "fd00::/80",
 	"cgroup-parent": "docker.slice",
-	"log-driver": "journald"
+	"log-driver": "journald",
+	"default-ulimits": {
+		"nofile": {
+			"Name": "nofile",
+			"Hard": 524288,
+			"Soft": 1024
+		}
+	}
 }