mlc_config.json: add file to ignore known troublesome URLs

This is the config file for the CI markdown link checker and lets us
filter URLs that are known to cause problems. Like
https://curl.zuul.vexxhost.dev/ for now.

Closes #8597

mlc_config.json

@@ -0,0 +1,8 @@
+{
+  "_comment": "Config file for linkcheck: If urls have some issues we can not fix on our end past it in here. MLC will ignore this.",
+  "ignorePatterns": [
+    {
+      "pattern": "^https://curl.zuul.vexxhost.dev"
+    }
+  ]
+}