Enhancement 🐞 report: implement the ability to unset the logo of the web via `spo web set`

### Description

At the moment the `spo web set` command can only be used to set the logo, but not to unset it.

### Steps to reproduce

`spo web set --siteLogoUrl ""`

### Expected result

The logo on the current web should be unset.

### Actual result

Just runs the command, but nothing changed.