Implement stream metadata augmentation in source adapters

[bwsw]

This is an optional feature. If ETCD_ENDPOINTS are not specified works without Etcd subscription.

Every stream adapter implementing single stream generation must be able to use the augmentation of video frames and messages with data stored in Etcd.

The source subscribes to the Etcd node with two subnodes:

• routing labels;
• video frame update.

• Etcd endpoints (ETCD_ENDPOINTS);
• Etcd credentials (ETCD_USERNAME, ETCD_PASSWORD);
• Etcd TLS files (ETCD_CA_CERT, ETCD_CLIENT_CERT, ETCD_CLIENT_KEY);
• Subscription node (ETCD_WATCH_NODE);
• Labels node (ETCD_MESSAGE_ROUTING_LABELS_NODE);
• Video frame update node (ETCD_VIDEO_FRAME_UPDATE_NODE);
• Video frame update format (PB, JSON, YAML) (ETCD_VIDEO_FRAME_UPDATE_FORMAT);
• Connect timeout (ETCD_CONNECT_TIMEOUT);
• Watch path initial wait timeout (ETCD_WATCH_PATH_INITIAL_WAIT_TIMEOUT).