Feature request: Advertise and publish messages from panel context for non-live data

[bgromov]

At the moment context.advertise() method is undefined when replaying data from MCAP. It would be great to be able to generate new data/topics from a panel extension.

Our use cases

1. We have an MCAP file with inertial and GPS data, and a panel extension that interfaces with a WASM library that does the sensor fusion. We are able to read and process the data but can't publish the result (e.g. in the form of Odometry message) because advertise() and publish() methods are not available for MCAP datasource.

   On the other hand, User Scripts can do that but they don't support 3rd-party modules, so we can't load WASM there.

2. We store sensor configuration (mounting pose) in the MCAP attachment and need to publish it as a transform to /tf topic.

Thanks!