Fffmpeg does not scale. about pymp

[tomp736]

Implement Queue using redis lists with lpop and rpush.

https://redis.io/docs/data-types/lists/

• add a new redis data access class (RedisMediaProcessQueue) that uses a redis list along with rpop and lpush methods implemented. The list elements will be media_info objects.
• during the existing scan that is done by the media_registry service, it will push media_info items onto the queue if they need to be processed (meaning, the media has no thumbnail or metadata present).
• during the existing scan that is done by the ffmpeg service, it will pop media_info from the new redis list and process the media.