docs: Suggestion - mention running multipass vm manually with console to diagnose start up issues

*Please describe the question or issue you're facing with "Troubleshoot launch/start issues - Multipass documentation".*

I had an issue where the vm would start, but not get a network connection. It turned out to be an issue with the virtual disk which wasn't clear because mutlipass doesn't show the console. I ran the qemu command manually without the -serial chardev:char0 -nographic options and was able to repair the disk.

---
*Reported from: https://documentation.ubuntu.com/multipass/latest/how-to-guides/troubleshoot/troubleshoot-launch-start-issues/*

Open the linked “Troubleshoot launch/start issues” documentation page and review how launch failures are currently diagnosed. Document the manual QEMU-console approach described in the issue, including removing -serial chardev:char0 -nographic so the virtual disk can be inspected or repaired. Done when the page explains this diagnostic path clearly.

Written by the indexing model from the issue text.