Docs: sudo is required on the apt-key add not on wget (#18180)

Running the command as given in the current doc throws the error:

```
sudo wget -q -O - https://packages.grafana.com/gpg.key | apt-key add -
ERROR: This command can only be used by root.
```

The proposed change fixes this issue.

docs/sources/installation/debian.md

@@ -51,7 +51,7 @@ sudo add-apt-repository "deb https://packages.grafana.com/oss/deb beta main"
 Use the above line even if you are on Ubuntu or another Debian version. Then add our gpg key. This allows you to install signed packages.
 
 ```bash
-sudo wget -q -O - https://packages.grafana.com/gpg.key | apt-key add -
+wget -q -O - https://packages.grafana.com/gpg.key | sudo apt-key add -
 ```
 
 Update your Apt repositories and install Grafana