Allow passing RTMP credentials inside the authentication part of the URL

[aler9]

Describe the feature

Support using URLs like:

rtmp://user:pass@host/mypath

[aler9]

This can't be done since authentication must be performed just after the RTMP connect command. At this stage, the server doesn't know neither the URL nor the action (reading, publishing) that the client wants to do.

Reference:

https://github.com/FFmpeg/FFmpeg/blob/f23e3ce8589629623db978ad70967eb37f7fac35/libavformat/rtmpproto.c#L1818