channels: let subscriber send webxdc updates to channel owner

[r10s]

to push webxdc for channels forward, we should allow subscribers to send updates.

that way, the channel owner will get the full state only, but that is fine for now, as they is the only who can send a webxdc, and can send webxdc known to make sense - already today, things as polls of games make sense - the highscore could be distributed.

this issue is only about the basic update sending.

in a subsequent iteration, we can consider special webxdc that then can distribute the state (for that, the webxdc probably need to know it is a channel owner)

cmp #7678, #7680

cc @Hocuri

[Simon-Laux]

and can send webxdc known to make sense

how would they know which webxdc makes sense for that? should we add a filter to the store, so integrated app selector only shows apps that make sense? (for example via metadata key in manifest) or is it irrelevant as long as channels are experimental?

[Hocuri]

I'd say it's irrelevant as long as channels are experimental.

[Simon-Laux]

Related note: webxdc updates of the owner also need to be sent to the subscribers, if that is not the case yet. Because to configure the poll app for example you need to send an initial update with the poll questions and settings. even if this already works in channels, it would make sense to add a test that tests it explicitly for the channel usecase.