Add a test for a site exclusion

### Issue Details

For a misbehaving domain, it's unclear whether it's tunnelled through the VPN connection or is accessed directly. I certainly can view the site exclusions, but if the list spans several screens, it takes minutes to find a suitable mask there.

### Proposed solution

Add a subcommand `test`:

```
Test whether a URL or an IP address is in the exclusions
Usage: adguardvpn-cli site-exclusions test [OPTIONS] url

Positionals:
url TEXT REQUIRED A URL, a domain name, or an IP address to test
```

A user may quickly copy a URL from a browser or enter a domain name or an IP address to see which way a request goes, directly or through a VPN connection.

### Alternative solution

The testing might be a top-level command, next to `login`, `status`, `config`, and so on. But I don't suppose the function is of _this_ great importance.