Add ability to specify recordings folder in AudioBridge

[lminiero]

This extends the enable_recording feature added by @rajneeshksoni to the AudioBridge plugin in #2674, by adding an additional property, called record_dir, where you can specify where the .wav recordings should be stored. It's available both in room creation (API or jcfg file) and when using enable_recording: when provided, it makes record_file a relative path. Notice this only impacts .wav recordings, and not the individual recording via .mjr that we do support in the AudioBridge: it may make sense to enforce it for those too, but maybe later.

Tested briefly but it seems to be working for me, feedback welcome.

[rajneeshksoni]

I like function with "record_dir" this makes it much easier to use.
I tested it and found a issue if during enable_recoding only "record_dir" is provided and "record_file" is not provided, API return success, record_dir directory is created but audio file is generated in the location where janus is launched.
so either api should return error or we should handle default file with user specified record_dir.

[lminiero]

Good catch: record_dir with no record_file is definitely allowed, it must create the filename randomly using your code, but place it in that folder. I'll fix it shortly. Thanks for the feedback!

[lminiero]

The commit above shoud fix it (haven't tested though).

[rajneeshksoni]

Tested, now it is working fine.

[lminiero]

Ack, merging then.