software/fluentd: Refactor software types

Add a new wendelin-telecom-gateway software type to the fluentd software release for use with Wendelin Telecom.

Instead of having to input the whole configuration as an instance parameter, this software type only requires a few necessary parameters to complete a pre-defined configuration template, which makes deployment easier for this specific use case.

UPDATE: As per the discussions below, this has been changed to make wendelin-telecom-gateway a new, more generic default software type intended to be used as a Wendelin gateway.

The current default type is moved to a new expert type, allowing the use of a custom fluentd configuration as before.