Update the server URL on server address change

### Is your feature request related to a problem? Please describe.
Hi, I've changed the address of my NC server and set up a redirect to the new address. I was unable to change the URL in the app and had to re-add the account instead.

### Describe the solution you'd like
Since changing the URL from the app might be considered a security issue (#3877), I'd like to propose the app changing the URL automatically, when receiving "301 Moved Permanently" response from the server.

### Describe alternatives you've considered
Changing the URL manually via settings, but that is not available either.

### Additional context
It seems that the Desktop client has this functionality and has updated the URL on its own after my changes.