Document namespace deletion problem

[tiina303]

Is your feature request related to a problem?

https://posthogusers.slack.com/archives/C01PPBY3G6Q/p1635344876020400?thread_ts=1635342422.018000&cid=C01PPBY3G6Q

Describe the solution you'd like

Document it in our troubleshooting page, but instead of edit it would be better to have the patch command & we should check if anything else is laying around too.

• while we're at it documenting the migrations job sticking around too.

Describe alternatives you've considered

Additional context

Thank you for your feature request – we love each and every one!