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/configuration/settings/interfaces.go

@@ -0,0 +1,5 @@
+package settings
+
+type Warner interface {
+	Warn(message string)
+}