add warning to upgrading postgres docker compose docs

[kasimrafique]

In preparation to upgrading to 2024.6, I was following the docs and I dumped the database and took a backup of the database files - However I forgot to run docker compose down

So I proceeded to rm -rf ./database whilst authentik was still running 🤦 - completely my fault for not following the steps in the exact order. I did read the DANGER box so made sure I had a backup (thankfully).

I propose adding a warning box below the DANGER box just so other people don't accidentally make the same mistake.
The colour change of the box does really draw attention vs. the standard text.

I was thinking something along the lines of:

Warning

Ensure your authentik stack is stopped before proceeding

Any thoughts about this?