Troubleshooting guide

[MarkusH]

It would be useful to point out how to handle (common) issues that can occur while using the CrateDB operator.

Here's a non-exhaustive list of topics:

• [ ] Bootstrapping times out because the cluster doesn't come up
• [ ] Restart times out half-way through the process, because the cluster doesn't turn GREEN anymore
• [ ] Scaling times out half-way through the process, because there are too many nodes in the cluster