Add kick_all requests and possibility to remove PIN code to both Audiobridge and Streaming plugins

[mikaelnousiainen]

This PR adds the following features to both the Audiobridge and the Streaming plugins:

• A new kick_all request, which kicks and disconnects all participants in an Audiobridge room and disconnects all viewers/listeners in a Streaming plugin endpoint
• Option to remove an existing PIN code (by setting it to an empty string) from either an Audiobridge room or a Streaming plugin endpoint

Both of these features are very useful if one needs to be able to control the set of participants/viewers in these plugins for long-lived mountpoints and/or rooms.

My specific application is using these features for providing exclusive (reserved) access to audio streams by following this process:

1. Set a new PIN code to a Streaming plugin endpoint (or an Audiobridge room)
2. Distribute the new PIN code to the participants/viewers allowed to access these streams
3. Use the new kick_all requests to guarantee that there are no participants/viewers left after changing the PIN code
4. Allow the participants with the new PIN code to join/view
5. Once the exclusive access period is over, the PIN code is removed (set to empty string)

[lminiero]

Thanks! I think this may be useful in VideoRoom and TextRoom as well, so in case I'll work on a similar enhancement for those too should this be merged.

That said, I think this patch needs work. First of all, I don't think this new functionality is needed at all in the Streaming plugin, since we have a request called "disable" that is very similar, and so maybe just needs to be extended a bit if it doesn't do exactly what you need. For the AudioBridge, as I pointed out in the review below, I'd definitely cut down the potentially huge number of notifications you're generating.

I'll do a deeper code review after the patch is updated.

[lminiero]

Thanks! Added a few notes inline.

[mikaelnousiainen]

@lminiero Changes done, please have a look at the refcounts and mutexes, as I'm not 100% sure about the ordering.

Also, in Streaming plugin destroy event handling, there is mutex locking on session->mutex too, like this: https://github.com/meetecho/janus-gateway/pull/2978/files#diff-3d84c5c61736914d38e005f37baaecfa324295ff90a45962773a0cb90520f2beL4482

Is this needed with kick_all? I'm simply locking each individual session (s->mutex) for every viewer, as they are modified.

[lminiero]

Just as a quick note, I haven't forgotten about this! I'll have to review the use of mutexes as you suggested, and I'll do it in the next few days.

[lminiero]

Thanks for the changes! They all look fine to me. The note you see below is a memo to me, so something I have to fix in the existing code myself.

I'll make a couple of tests later, and in case I don't see issues, I'll merge 👍

[lminiero]

Thanks for the quick fix! Finally merging then 💪