utils: Add limits.d dir with sample config files

Same as the ones described in osmo-gsm-tester User Manual and same as
ones deployed by ansible scripts. Let's rather keep them here.

Change-Id: I8b124a8a1637666536772439b920e7b91e61533c
diff --git a/utils/limits.d/osmo-gsm-tester_allowcore.conf b/utils/limits.d/osmo-gsm-tester_allowcore.conf
new file mode 100644
index 0000000..5eee2f9
--- /dev/null
+++ b/utils/limits.d/osmo-gsm-tester_allowcore.conf
@@ -0,0 +1 @@
+@osmo-gsm-tester - core unlimited