docs: expose Jest Matchers migration guide in the sidebar (#1737)

Author: mdjastrzebski

website/docs/13.x/docs/migration/_meta.json

@@ -1 +1,5 @@
-["v13", { "type": "dir", "name": "previous", "label": "Previous versions", "collapsed": true }]
+[
+  "v13",
+  "jest-matchers",
+  { "type": "dir", "name": "previous", "label": "Previous versions", "collapsed": true }
+]