feat(config): allow invalid server filters (#2419)

- Disallow setting a server filter when there is no choice available
- Allow setting an invalid server filter when there is at least one choice available
- Log at warn level when an invalid server filter is set
- Fix #2337

internal/cli/openvpnconfig.go

@@ -59,7 +59,7 @@ func (c *CLI) OpenvpnConfig(logger OpenvpnConfigLogger, reader *reader.Reader,
 		return fmt.Errorf("checking for IPv6 support: %w", err)
 	}
 
-	if err = allSettings.Validate(storage, ipv6Supported); err != nil {
+	if err = allSettings.Validate(storage, ipv6Supported, logger); err != nil {
 		return fmt.Errorf("validating settings: %w", err)
 	}