Add new API to bulk start/stop MJR-based recordings in AudioBridge

[lminiero]

As the title says, this adds a feature that was missing in the AudioBridge, namely the ability to start/stop the recording of all participants to MJR files as we do have in the VideoRoom. In fact, while AudioBridge does have an enable_recording request just as the VideoRoom does, it uses that request to trigger the recorded mix, which is the default mechanism for recording a room in the AudioBridge: since the AudioBridge plugin can also be instructed to save the contributions of each participant to a separate MJR file as well, though (e.g., for external mixing and processing), then a request to enable/disable it for all participants in a room at the same time was helpful as well.

The syntax for the new request is basically the same as the existing enable_recording, with the difference that it is named differently, and references a different variable for the target folder. In fact, you can specify where MJR files should be saved by default by specifying an mjrs_dir when creating the room; the folder can be changed (for new recordings, not old or ongoing ones) using edit as well, or in the request that follows. Then, you can start/stop a bulk recording to MJR using the following request:

{
	"request" : "enable_mjrs",
	"room" : <unique numeric ID of the room>,
	"secret" : "<room secret; mandatory if configured>"
	"mjrs" : <true|false, whether all participants in the room should be individually recorded to mjr files or not>,
	"mjrs_dir" : "<path where all MJR files should be saved to (optional)>"
}

I plan to merge soon, so feedback welcome!

[lminiero]

Merging ✌️