Move common markdownlint config to top-level file

.markdownlint.json

@@ -0,0 +1,4 @@
+{
+  "MD013": false,
+  "MD041": false
+}

extensions/ql-vscode/.markdownlint-cli2.cjs

@@ -1,7 +1,12 @@
-const options = require('@github/markdownlint-github').init({
-  "MD013": false, // Line length
-  "MD041": false, // First line in file should be a top level heading
-})
+// Having the base options in a top-level config file means
+// that the extension can pick them up too, since that only
+// considers _this_ file when looking at files in this directory
+// or below.
+base_options = require('../../.markdownlint.json')
+
+const options = require('@github/markdownlint-github').init(
+  base_options
+)
 module.exports = {
     config: options,
     customRules: ["@github/markdownlint-github"],