docs: add MySQL to navigation menu

Fixes content check error by adding mysql.mdx to docs navigation.
   MySQL page now appears in Commands > connect section alongside postgres.

website/data/docs-nav-data.json

@@ -944,6 +944,10 @@
             "title": "kube",
             "path": "commands/connect/kube"
           },
+          {
+            "title": "mysql",
+            "path": "commands/connect/mysql"
+          },
           {
             "title": "postgres",
             "path": "commands/connect/postgres"