Add troubleshooting section for MongoDB docs

Author: jchristgit

ansible/roles/mongodb/README.md

@@ -3,3 +3,27 @@
 This role deploys MongoDB using podman quadlets.
 
 The container starts as root, but drops privileges after startup.
+
+
+## Troubleshooting
+
+- **MongoDB refuses connections**
+
+  Verify that:
+
+  1. Your outbound IP is within the whitelisted LKE ranges in `/etc/nftables` -
+     the `nftables` Ansible role may be re-run to fetch them freshly
+
+  2. Your outbound IP is not banned by `fail2ban`, see `fail2ban-client banned`
+
+  3. You are using a sane piece of software that does not randomly appear to not
+     bind on ports properly:
+
+     > I encountered the same problem for an half an hour or so but it was not
+     > an issue after that. I changed nothing in my code or my firewall
+     > settings. Just waited a bit and the program worked as usual. So I think
+     > this may be something that is wrong with the Mongodb servers or it may be
+     > due to a slow network connection. Maybe check the uri and just waiting
+     > for a while. It worked for me.
+
+     When in doubt, `sudo systemctl restart mongodb`