Add Update Instructions

### Please agree to the following

- [X] I have searched [existing issues](https://github.com/cryptomator/hub/issues?q=) for duplicates
- [X] I agree to follow this project's [Code of Conduct](https://github.com/cryptomator/hub/blob/develop/.github/CODE_OF_CONDUCT.md)

### Summary

Show update instructions from admin UI

### Motivation

When seeing that an update is available, I might not know what to do with this information. I would expect to be able to click somewhere to get instructions.

It might be useful for Hub to know, if it is deployed using Kubernetes or Docker Compose to show tailored instructions. We could introduce additional `HUB_` env vars.

### Considered Alternatives

Linking to the documentation is the least we can do. However needing documentation just to update software suggests it to be a fairly complicated process. Let's avoid this.

### Anything else?

When using floating tags such as `beta` or `stable` (see #120), updating is fairly easy. E.g. on Kubernetes this is all you need to do:

```
kubectl rollout restart deployment cryptomator-hub -n myCustomNamespace
```