[PubSub] Support for PubSub Specification v 1.05.04

[jnsjll]

Currently, it seems that the PubSub implementation does not support some of the new functionality specified in PubSub Specification v 1.05.04 like DiscoveryMessages (except for MetaData).
For instance, for MQTT the specification states about status discovery messages:

A Publisher that is exclusively using a PublisherId shall register a Status message as an MQTT Will message when it creates the connection to the MQTT Broker. This message is sent automatically if the Publisher loses its connection with the MQTT Broker. The IsCyclic shall be FALSE in this case. The PubSubState value of the Will message shall be Error.

[...] In these cases, the Publisher sends updates only when its state changes and the Message Oriented Middleware will send an update with PubSubState Error if the Publisher goes offline.

Are there plans to support that in the future?

[romanett]

@jnsjll I don't think the working group currently plans to add this. However if you provide some smaller Pull Requests adding missing functionality we could probably include these updates.

[romanett]

Feel free to Open Issues for Missing Features however so we have an Overview of Missing functionality