TopicViewer doesn't introspect custom protobuf messages

[caguero]

The main reason for this issue is the inability to receive an unknown serialized protobuf message and unserialize it into a generic protobuf message. Protobuf requires to cast the message into a specific type and this type is not known by Ignition Transport from the TopicViewer.

An alternative solution might be to generate our custom messages with descriptor information (--descriptor_set_out) and use DynamicMessage to manipulate the message at runtime. Another solution might be to specify the path of the proto files at runtime and check if there are Protobuf utilities to generate a message on the fly based on the proto messages found.

There's some research to do here.

[caguero]

Here's a first implementation in Ignition Msgs.